Document missing Socket APIs (dotnet#7153)

* add missing summaries

* SendPacketsElement remarks

* add TcpListener remarks

* fix Buffer remarks

Author: antonfirsov

xml/System.Net.Sockets/SendPacketsElement.xml

@@ -163,9 +163,16 @@
         <Parameter Name="buffer" Type="System.ReadOnlyMemory&lt;System.Byte&gt;" Index="0" FrameworkAlternate="net-6.0" />
       </Parameters>
       <Docs>
-        <param name="buffer">To be added.</param>
-        <summary>To be added.</summary>
-        <remarks>To be added.</remarks>
+        <param name="buffer">A <see cref="T:System.ReadOnlyMemory`1" /> of bytes to send using the <see cref="M:System.Net.Sockets.Socket.SendPacketsAsync(System.Net.Sockets.SocketAsyncEventArgs)" /> method.</param>
+        <summary>Initializes a new instance of the <see cref="T:System.Net.Sockets.SendPacketsElement" /> class using the specified buffer.</summary>
+        <remarks>
+          <format type="text/markdown"><![CDATA[  
+  
+## Remarks  
+ The <xref:System.Net.Sockets.SendPacketsElement> class is used with the <xref:System.Net.Sockets.SocketAsyncEventArgs.SendPacketsElements%2A?displayProperty=nameWithType> property to get or set a data buffer or file to be sent using the <xref:System.Net.Sockets.Socket.SendPacketsAsync%2A?displayProperty=nameWithType> method.  
+  
+ ]]></format>
+        </remarks>
       </Docs>
     </Member>
     <Member MemberName=".ctor">
@@ -244,10 +251,17 @@
         <Parameter Name="endOfPacket" Type="System.Boolean" Index="1" FrameworkAlternate="net-6.0" />
       </Parameters>
       <Docs>
-        <param name="buffer">To be added.</param>
-        <param name="endOfPacket">To be added.</param>
-        <summary>To be added.</summary>
-        <remarks>To be added.</remarks>
+        <param name="buffer">A <see cref="T:System.ReadOnlyMemory`1" /> of bytes to send using the <see cref="M:System.Net.Sockets.Socket.SendPacketsAsync(System.Net.Sockets.SocketAsyncEventArgs)" /> method.</param>
+        <param name="endOfPacket">Specifies that this element should not be combined with the next element in a single send request from the sockets layer to the transport. This flag is used for granular control of the content of each message on a datagram or message-oriented socket.</param>
+        <summary>Initializes a new instance of the <see cref="T:System.Net.Sockets.SendPacketsElement" /> class using the specified buffer with an option to combine this element with the next element in a single send request from the sockets layer to the transport.</summary>
+        <remarks>
+          <format type="text/markdown"><![CDATA[  
+  
+## Remarks  
+ The <xref:System.Net.Sockets.SendPacketsElement> class is used with the <xref:System.Net.Sockets.SocketAsyncEventArgs.SendPacketsElements%2A?displayProperty=nameWithType> property to get or set a data buffer or file to be sent using the <xref:System.Net.Sockets.Socket.SendPacketsAsync%2A?displayProperty=nameWithType> method.  
+  
+ ]]></format>
+        </remarks>
       </Docs>
     </Member>
     <Member MemberName=".ctor">
@@ -717,7 +731,9 @@
           <format type="text/markdown"><![CDATA[  
   
 ## Remarks  
- The default value for the <xref:System.Net.Sockets.SendPacketsElement.Buffer> property is `null` if the <xref:System.Net.Sockets.SendPacketsElement> object was not initialized with a `buffer` parameter.  
+ The default value for the <xref:System.Net.Sockets.SendPacketsElement.Buffer> property is `null` if the <xref:System.Net.Sockets.SendPacketsElement> object was not initialized with a `buffer` parameter or `buffer` was passed as a <xref:System.ReadOnlyMemory`1> of bytes.
+
+ In the latter case, the buffer can be obtained using the <xref:System.Net.Sockets.SendPacketsElement.MemoryBuffer> property.
   
  ]]></format>
         </remarks>
@@ -927,9 +943,17 @@
         <ReturnType>System.Nullable&lt;System.ReadOnlyMemory&lt;System.Byte&gt;&gt;</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>To be added.</summary>
-        <value>To be added.</value>
-        <remarks>To be added.</remarks>
+        <summary>Gets the buffer to be sent if the <see cref="T:System.Net.Sockets.SendPacketsElement" /> object was initialized with a <code>buffer</code> parameter.</summary>
+        <value>The <see cref="T:System.ReadOnlyMemory`1" /> of bytes to be sent if the <see cref="T:System.Net.Sockets.SendPacketsElement" /> object was initialized with a <code>buffer</code> parameter.</value>
+        <remarks>
+          <format type="text/markdown"><![CDATA[  
+  
+## Remarks  
+ The default value for the <xref:System.Net.Sockets.SendPacketsElement.MemoryBuffer> property is `null` if the <xref:System.Net.Sockets.SendPacketsElement> object was not initialized with a `buffer` parameter.
+ If `buffer` was passed as a `byte[]`, <xref:System.Net.Sockets.SendPacketsElement.MemoryBuffer> returns the contents of <xref:System.Net.Sockets.SendPacketsElement.Buffer> as a <xref:System.ReadOnlyMemory`1> of bytes.
+  
+ ]]></format>
+        </remarks>
       </Docs>
     </Member>
     <Member MemberName="Offset">

xml/System.Net.Sockets/TcpListener.xml

@@ -423,10 +423,22 @@
         <Parameter Name="cancellationToken" Type="System.Threading.CancellationToken" Index="0" FrameworkAlternate="net-6.0" />
       </Parameters>
       <Docs>
-        <param name="cancellationToken">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
-        <remarks>To be added.</remarks>
+        <param name="cancellationToken">A cancellation token that can be used to cancel the asynchronous operation.</param>
+        <summary>Accepts a pending connection request as a cancellable asynchronous operation.</summary>
+        <returns>The task object representing the asynchronous operation. The <see cref="P:System.Threading.Tasks.Task`1.Result" /> property on the task object returns a <see cref="T:System.Net.Sockets.Socket" /> used to send and receive data.</returns>
+        <remarks>
+          <format type="text/markdown"><![CDATA[  
+  
+## Remarks  
+ This operation will not block. The returned <xref:System.Threading.Tasks.Task%601> object will complete after the socket connection has been accepted.  
+  
+ The <xref:System.Net.Sockets.Socket> returned in <xref:System.Threading.Tasks.Task%601> is initialized with the IP address and port number of the remote host. You can use any of the <xref:System.Net.Sockets.Socket.Send%2A> and <xref:System.Net.Sockets.Socket.Receive%2A> methods available in the <xref:System.Net.Sockets.Socket> class to communicate with the remote host. When you are finished using the <xref:System.Net.Sockets.Socket>, be sure to call its <xref:System.Net.Sockets.Socket.Close%2A> method. If your application is relatively simple, consider using the <xref:System.Net.Sockets.TcpListener.AcceptTcpClient%2A> method rather than the <xref:System.Net.Sockets.TcpListener.AcceptSocketAsync%2A> method. <xref:System.Net.Sockets.TcpClient> provides you with simple methods for sending and receiving data over a network in blocking synchronous mode.  
+  
+> [!NOTE]
+>  This member outputs trace information when you enable network tracing in your application. For more information, see [Network Tracing in the .NET Framework](/dotnet/framework/network-programming/network-tracing).  
+  
+ ]]></format>
+        </remarks>
       </Docs>
     </Member>
     <Member MemberName="AcceptTcpClient">
@@ -571,10 +583,22 @@
         <Parameter Name="cancellationToken" Type="System.Threading.CancellationToken" Index="0" FrameworkAlternate="net-6.0" />
       </Parameters>
       <Docs>
-        <param name="cancellationToken">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
-        <remarks>To be added.</remarks>
+        <param name="cancellationToken">A cancellation token that can be used to cancel the asynchronous operation</param>
+        <summary>Accepts a pending connection request as a cancellable asynchronous operation.</summary>
+        <returns>The task object representing the asynchronous operation. The <see cref="P:System.Threading.Tasks.Task`1.Result" /> property on the task object returns a <see cref="T:System.Net.Sockets.TcpClient" /> used to send and receive data.</returns>
+        <remarks>
+          <format type="text/markdown"><![CDATA[  
+  
+## Remarks  
+ This operation will not block. The returned <xref:System.Threading.Tasks.Task%601> object will complete after the TCP connection has been accepted.  
+  
+ Use the <xref:System.Net.Sockets.TcpClient.GetStream%2A?displayProperty=nameWithType> method to obtain the underlying <xref:System.Net.Sockets.NetworkStream> of the returned <xref:System.Net.Sockets.TcpClient> in the <xref:System.Threading.Tasks.Task%601>. The <xref:System.Net.Sockets.NetworkStream> will provide you with methods for sending and receiving with the remote host. When you are through with the <xref:System.Net.Sockets.TcpClient>, be sure to call its <xref:System.Net.Sockets.TcpClient.Close%2A> method. If you want greater flexibility than a <xref:System.Net.Sockets.TcpClient> offers, consider using <xref:System.Net.Sockets.TcpListener.AcceptSocket%2A> or <xref:System.Net.Sockets.TcpListener.AcceptSocketAsync%2A>.  
+  
+> [!NOTE]
+>  This member outputs trace information when you enable network tracing in your application. For more information, see [Network Tracing in the .NET Framework](/dotnet/framework/network-programming/network-tracing).  
+  
+ ]]></format>
+        </remarks>
       </Docs>
     </Member>
     <Member MemberName="Active">