s3:messaging: change messaging_backend to use iovec instead of data blob in send_fn

This also changes the layering

messaging_send_iov -> messaging_send_buf -> messaging_send

to

messaging_send_buf -> messaging_send -> messaging_send_iov

Signed-off-by: Michael Adam <obnox@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
s3:messaging: change unix_dgram_recv_handler() to use recvmsg, not recv

This is in preparation of adding fd-passing to messaging.

Signed-off-by: Michael Adam <obnox@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>

Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Fri May 30 02:28:15 CEST 2014 on sn-devel-104