channeld: Send a depth=0 notification when channeld starts up

This is used in order to ensure zeroconf doesn't just wait for the
first confirmation despite mindepth being set to 0.

lightningd/channel_control.c

@@ -783,6 +783,13 @@ void peer_start_channeld(struct channel *channel,
 		try_update_blockheight(ld, channel,
 				       get_block_height(ld->topology));
 	}
+
+	/* Artificial confirmation event for zeroconf */
+	if (channel_type_has(channel->type, OPT_ZEROCONF))
+		subd_send_msg(
+		    channel->owner,
+		    take(towire_channeld_funding_depth(
+			NULL, channel->scid, channel->alias[LOCAL], 0)));
 }
 
 bool channel_tell_depth(struct lightningd *ld,