s3:cleanupd: use MSG_SMB_BRL_VALIDATE to signal cleanupd unclean process shutdown

s3:cleanupd: use MSG_SMB_BRL_VALIDATE to signal cleanupd unclean process shutdown

Since 6423ca4bf293cac5e2f84b1a37bb29b06b5c05ed messaging_send_all()
broadcasts messages in a cluster, so cleanupd receives those broadcasts
and acts upon it by re-broadcasting the message. Result: message
storm.

By reactivating the currently unused MSG_SMB_BRL_VALIDATE for the
trigger message to cleanupd we avoid the storm.

Note that MSG_SMB_BRL_VALIDATE was unused only in the sense that noone
*listened* to it, but we were still *sending* the message in
smbd_parent_ctdb_reconfigured(). de6fe2a1dd6ab03b1c369b61da17fded72305b2d
removed listening for MSG_SMB_BRL_VALIDATE from cleanupd. This commits
brings it back.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=13414

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>