Add Socket missing API (#4762)

Co-authored-by: Jan Jahoda <[email protected]>

Author: Jan Jahoda

xml/System.Net.Sockets/Socket.xml

@@ -6669,8 +6669,9 @@ The maximum length of the pending connections queue is determined automatically.
         <ReturnType>System.Boolean</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>To be added.</summary>
-        <value>To be added.</value>
+        <summary>Indicates whether the underlying operating system support the Unix domain sockets.</summary>
+        <value>
+          <see langword="true" /> if the operating system support the Unix domain sockets; otherwise, <see langword="false" />.</value>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>