gossip: Limit announcement sigs reply

A splice where reestablish happens at the right moment causes an infinite loop of announcement signatures being sent back and forth.

Limit the announcement sigs we send in response to announcement sigs to once per channel session.

ChangelogNone

lightningd/channel.c

@@ -322,6 +322,7 @@ struct channel *new_unsaved_channel(struct peer *peer,
 	/* Nothing happened yet */
 	memset(&channel->stats, 0, sizeof(channel->stats));
 	channel->state_changes = tal_arr(channel, struct channel_state_change *, 0);
+	channel->replied_to_announcement_sigs = false;
 
 	/* No shachain yet */
 	channel->their_shachain.id = 0;
@@ -632,6 +633,7 @@ struct channel *new_channel(struct peer *peer, u64 dbid,
 	channel->num_onchain_spent_calls = 0;
 	channel->stats = *stats;
 	channel->state_changes = tal_steal(channel, state_changes);
+	channel->replied_to_announcement_sigs = false;
 
  	/* Populate channel->channel_gossip */
 	channel_gossip_init(channel, take(peer_update));

lightningd/channel.h

@@ -353,6 +353,9 @@ struct channel {
 
 	/* Our change history. */
 	struct channel_state_change **state_changes;
+
+	/* Have we replied to announcement_signatures once? */
+	bool replied_to_announcement_sigs;
 };
 
 /* Is channel owned (and should be talking to peer) */

lightningd/channel_gossip.c

@@ -688,7 +688,10 @@ void channel_gossip_got_announcement_sigs(struct channel *channel,
 		 *       - MUST respond with its own `announcement_signatures`
 		 *        message.
 		 */
-		send_channel_announce_sigs(channel);
+		if(!channel->replied_to_announcement_sigs) {
+			send_channel_announce_sigs(channel);
+			channel->replied_to_announcement_sigs = true;
+		}
 		check_channel_gossip(channel);
 		return;
 	}