Retransmit announcement_signatures if requested

The previous commit allowed requesting retransmission of
announcement_signatures during channel reestablishment. This commit
handles such requests.

Author: jkczyz

lightning/src/ln/channel.rs

@@ -8718,6 +8718,20 @@ where
 
 		let shutdown_msg = self.get_outbound_shutdown();
 
+		// A receiving node:
+		//   - if `my_current_funding_locked` is included with the `announcement_signatures` bit
+		//     set in the `retransmit_flags`:
+		//     - if `announce_channel` is set for this channel and the receiving node is ready
+		//       to send `announcement_signatures` for the corresponding splice transaction:
+		//       - MUST retransmit `announcement_signatures`.
+		if let Some(funding_locked) = &msg.my_current_funding_locked {
+			if funding_locked.should_retransmit(msgs::RetransmitFlag::AnnouncementSignatures) {
+				if self.funding.get_funding_txid() == Some(funding_locked.txid) {
+					self.context.announcement_sigs_state = AnnouncementSigsState::NotSent;
+				}
+			}
+		}
+
 		let announcement_sigs = self.get_announcement_sigs(node_signer, chain_hash, user_config, best_block.height, logger);
 
 		if matches!(self.context.channel_state, ChannelState::AwaitingChannelReady(_)) {

lightning/src/ln/msgs.rs

@@ -954,6 +954,11 @@ impl FundingLocked {
 	pub fn retransmit(&mut self, flag: RetransmitFlag) {
 		self.retransmit_flags |= 1 << flag as u8;
 	}
+
+	/// Returns whether the message corresponding to `flag` should be retransmitted.
+	pub fn should_retransmit(&self, flag: RetransmitFlag) -> bool {
+		self.retransmit_flags & (1 << flag as u8) != 0
+	}
 }
 
 /// Bit positions used in [`FundingLocked::retransmit_flags`] for requesting message retransmission.