Cannot use IPv6 in Unity

[xmedeko]

The NetSocket.Bind to IPv6 fails on Unity, we have error:
System.Net.Sockets.SocketException (0x80004005): Only one usage of each socket address (protocol/network address/port) is normally permitted

If we remove #if !UNITY from code, so as the socket option is set:

socket.SetSocketOption(SocketOptionLevel.IPv6, (SocketOptionName) 27, true);

then the bind pass.

Library version: 0.8indev commit b86f288
Framework: Unity, Mono backend .NET 4.5
OS: Windows 10

Note: we do not use IPv6 at the moment. It would be nice to have NetManager flag not to bind to IPv6 at all.