[release/10.0] fix permissive Socket.DualMode

src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.cs

@@ -70,7 +70,7 @@ public partial class Socket : IDisposable
         private bool _disposed;
 
         public Socket(SocketType socketType, ProtocolType protocolType)
-            : this(OSSupportsIPv6DualMode ? AddressFamily.InterNetworkV6 : AddressFamily.InterNetwork, socketType, protocolType)
+            : this(OSSupportsIPv6 ? AddressFamily.InterNetworkV6 : AddressFamily.InterNetwork, socketType, protocolType)
         {
             if (OSSupportsIPv6DualMode)
             {
@@ -749,7 +749,7 @@ public bool DualMode
                 {
                     return false;
                 }
-                if (!OSSupportsIPv6DualMode)
+                if (OperatingSystem.IsWasi())
                 {
                     return false;
                 }
@@ -762,7 +762,7 @@ public bool DualMode
                     throw new NotSupportedException(SR.net_invalidversion);
                 }
 
-                if (!OSSupportsIPv6DualMode && value) throw new PlatformNotSupportedException();
+                if (OperatingSystem.IsWasi() && value) throw new PlatformNotSupportedException();
 
                 SetSocketOption(SocketOptionLevel.IPv6, SocketOptionName.IPv6Only, value ? 0 : 1);
             }

src/libraries/System.Net.Sockets/tests/FunctionalTests/OSSupport.cs

@@ -37,6 +37,14 @@ public async Task DisableIPv6_OSSupportsIPv6_False()
             static void RunTest()
             {
                 Assert.False(Socket.OSSupportsIPv6);
+
+                // related to https://github.com/dotnet/runtime/issues/122435
+                var listenSocket = new Socket(AddressFamily.InterNetworkV6, SocketType.Stream, ProtocolType.Tcp);
+                listenSocket.DualMode = true;
+
+                listenSocket.Bind(new IPEndPoint(IPAddress.IPv6Any, 0));
+                listenSocket.Listen(1);
+                listenSocket.Close();
             }
         }