TcpSocketChannel.DoConnect returning true stops channel active being fired

When using UnixEndPoint under Mono on Linux, TcpSocketChannel never becomes active after a call to connect. The reason appears to be that the connection succeeds immediately, on DoConnect returns false.

When creating a subclass (see attached code) which always returns false, then all is well. Also, when TcpSocketChannel tries to create a Socket, it always provides ProtocolType.IPv6. For unix domain sockets that needs to be ProtocolType.Unspecified otherwise an exception is thrown.

```csharp
using System.Net;
using System.Net.Sockets;
using DotNetty.Transport.Channels.Sockets;

namespace agentx
{
internal class UnixSocketChannel : TcpSocketChannel
{
public UnixSocketChannel()
: base(new Socket(AddressFamily.Unix, SocketType.Stream, ProtocolType.Unspecified))
{
}

protected override bool DoConnect(EndPoint remoteAddress, EndPoint localAddress)
{
base.DoConnect(remoteAddress, localAddress);

// channel never fires active event if indicates that connected already
return false;
}
}
}
```