messaging3: Avoid messaging_is_self_send

messaging3: Avoid messaging_is_self_send

This was a bad API, and it was used in a buggy way: In
messaging_dispatch_rec we always did the defer, we referenced the
destination pid, not the source. In messaging_send_iov this is the right
thing to do to reference the destination, but when we have arrived in
messaging_dispatch_rec we should compare source and destination.

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