added protocol family argument to Bind message

added new socket option to join a multicast group

This commit provides the means to specify the protocol family (e.g., IPv4 or IPv6) when an actor attempts to bind to a socket using IO(Udp). On systems that are dual stacked, the current implementation will prefer IPv6; preventing a socket from joining an IPv4 multicast group.
If that line will never be called, it means that the catch-clause is never going to be invoked, and in which case is it then needed?