libsmb: Make sure that the TCP socket is non-blocking

libsmb: Make sure that the TCP socket is non-blocking

All traffic goes through smbXcli_base.c, and that is prepared to deal
with short writes via the conn->outgoing queue. Instead of making sure
that all callers properly set the socket nonblocking, do it here, so
that we can later optimize sending out data to the server.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>