s4:lib/socket: add socket_connect_multi_ex_*

s4:lib/socket: add socket_connect_multi_ex_*

This add an async establish hook, that gets called
before a connection success is detected.

This can be used to do a NBT session request
and it makes sure that we don't cancel the connection
on port 445, just because the tcp connect on port
139 worked.

metze