rpc_server: Don't rely on TCP-bind() to return EADDRINUSE

rpc_server: Don't rely on TCP-bind() to return EADDRINUSE

socket_wrapper can't do EADDRINUSE because unix domain sockets don't
do it.

This currently works correctly because right now all RPC servers
either use explicit ports or all listen on the same socket.

The new code uses a static variable, so it only helps if a single
process listens for multiple RPC sockets. It won't work if multiple
processes start listening. But in case samba-dcerpcd goes in this will
be exactly the right thing to do.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>