channel: Defer sending the announcement_signature until both lock

We were sending the announcement_signatures as soon as we locally
locked and got the announcement_depth, this doesn't make the channel
usable any sooner and forces the other side to stash the
signature. This defers the announcement_signature until the channel
really is usable.

This is done by adding an additional check for the remote locked
message and adding a trigger on remote lock.

Signed-off-by: Christian Decker <decker.christian@gmail.com>

channeld/channel.c

@@ -183,7 +183,9 @@ static void send_announcement_signatures(struct peer *peer)
 	 * `funding_locked` has been sent and the funding transaction has
 	 * at least 6 confirmations.
 	 */
-	if (!(peer->announce_depth_reached && peer->funding_locked[LOCAL]))
+	/* Actually defer a bit further until both ends have signaled */
+	if (!peer->announce_depth_reached || !peer->funding_locked[LOCAL] ||
+	    !peer->funding_locked[REMOTE])
 		return;
 
 	tmpctx = tal_tmpctx(peer);
@@ -1692,6 +1694,8 @@ static void handle_funding_locked(struct peer *peer, const u8 *msg)
 	msg_enqueue(&peer->peer_out, take(msg));
 	peer->funding_locked[LOCAL] = true;
 
+	send_announcement_signatures(peer);
+
 	if (peer->funding_locked[REMOTE]) {
 		wire_sync_write(MASTER_FD,
 				take(towire_channel_normal_operation(peer)));