smbd: Fix a talloc hierarchy problem in msg_channel

smbd: Fix a talloc hierarchy problem in msg_channel

When tearing down a watch_send with an open tevent_immediate, we
talloc_free the msg_channel while the tevent_immediate still references
it. Don't make the tevent_immediate outlive the msg_channel.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=10250
Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Wed Nov 20 00:13:51 CET 2013 on sn-devel-104