IPInterfaceProperties.GetIPv(4|6)Properties never returns null (dotnet#11056)

The null checking in the code samples is unnecessary and misleading so I'm proposing to delete it. Moreover, we should call out in the remarks section the necessity of a capability check so users avoid walking into an exception in case of missing protocol support.

Author: antonfirsov

snippets/cpp/VS_Snippets_Remoting/NCLNetInfo2/CPP/networkexamples.cpp

@@ -836,11 +836,6 @@ void DisplayIPv4NetworkInterfaces()
 
       // Try to get the IPv4 interface properties.
       IPv4InterfaceProperties ^ p = adapterProperties->GetIPv4Properties();
-      if ( !p )
-      {
-         Console::WriteLine( "No IPv4 information is available for this interface." );
-         continue;
-      }
 
       // Display the IPv4 specific data.
       Console::WriteLine( "  Index ............................. : {0}", 

snippets/csharp/System.Net.NetworkInformation/DuplicateAddressDetectionState/Overview/networkexamples.cs

@@ -796,12 +796,6 @@ public static void DisplayIPv4NetworkInterfaces()
                 // Try to get the IPv4 interface properties.
                 IPv4InterfaceProperties p = adapterProperties.GetIPv4Properties();
 
-                if (p == null)
-                {
-                    Console.WriteLine("No IPv4 information is available for this interface.");
-                    Console.WriteLine();
-                    continue;
-                }
                 // Display the IPv4 specific data.
                 Console.WriteLine("  Index ............................. : {0}", p.Index);
                 Console.WriteLine("  MTU ............................... : {0}", p.Mtu);

snippets/visualbasic/VS_Snippets_Remoting/NCLNetInfo2/VB/networkexamples.vb

@@ -695,11 +695,7 @@ Public Class NetworkingExample
             Dim adapterProperties As IPInterfaceProperties = adapter.GetIPProperties()
             ' Try to get the IPv4 interface properties.
             Dim p As IPv4InterfaceProperties = adapterProperties.GetIPv4Properties()
-            
-            If p Is Nothing Then
-                Console.WriteLine("No IPv4 information is available for this interface.")
-                GoTo ContinueForEach1
-            End If
+
             ' Display the IPv4 specific data.
             Console.WriteLine("  Index ............................. : {0}", p.Index)
             Console.WriteLine("  MTU ............................... : {0}", p.Mtu)

xml/System.Net.NetworkInformation/IPInterfaceProperties.xml

@@ -494,7 +494,8 @@
   
 ## Remarks  
  For a detailed description of the information available for an interface that supports IPv4, see the <xref:System.Net.NetworkInformation.IPv4InterfaceProperties> class documentation. Note that the object returned by the <xref:System.Net.NetworkInformation.IPInterfaceProperties.GetIPv4Properties%2A> method reflects the configuration as of the time the object is created. This information is not updated dynamically.  
-  
+ A <xref:System.Net.NetworkInformation.NetworkInformationException> is thrown if the interface does not support the IPv4 protocol, therefore it's recommended to check IPv4 support calling <xref:System.Net.NetworkInformation.NetworkInterface.Supports%2A> on the originating <xref:System.Net.NetworkInformation.NetworkInterface> instance before querying the IPv4 properties.
+
  ]]></format>
         </remarks>
         <exception cref="T:System.Net.NetworkInformation.NetworkInformationException">The interface does not support the IPv4 protocol.</exception>
@@ -544,7 +545,8 @@
   
 ## Remarks  
  For a detailed description of the information available for an interface that supports IPv6, see the <xref:System.Net.NetworkInformation.IPv6InterfaceProperties> documentation. Note that the object returned by the <xref:System.Net.NetworkInformation.IPInterfaceProperties.GetIPv6Properties%2A> method reflects the configuration as of the time the object is created. This information is not updated dynamically.  
-  
+ A <xref:System.Net.NetworkInformation.NetworkInformationException> is thrown if the interface does not support the IPv6 protocol, therefore it's recommended to check IPv6 support calling <xref:System.Net.NetworkInformation.NetworkInterface.Supports%2A> on the originating <xref:System.Net.NetworkInformation.NetworkInterface> instance before querying the IPv6 properties.
+ 
  ]]></format>
         </remarks>
         <exception cref="T:System.Net.NetworkInformation.NetworkInformationException">The interface does not support the IPv6 protocol.</exception>