Avoid initial commitment channel_ready retransmission while splicing

If nodes have started a splice, this means they have both sent and
received `channel_ready` already: in that case, it's unnecessary to
retransmit `channel_ready` on reconnection.

Author: wpaulino

lightning/src/ln/channel.rs

@@ -9693,12 +9693,46 @@ where
 
 		// A node:
 		//   - if `next_commitment_number` is 1 in both the `channel_reestablish` it
-		//     sent and received:
+		//     sent and received, and none of those `channel_reestablish` messages
+		//     contain `my_current_funding_locked` or `next_funding` for a splice transaction:
 		//     - MUST retransmit `channel_ready`.
 		//   - otherwise:
 		//     - MUST NOT retransmit `channel_ready`, but MAY send `channel_ready` with
 		//       a different `short_channel_id` `alias` field.
-		let channel_ready = if msg.next_local_commitment_number == 1 && INITIAL_COMMITMENT_NUMBER - self.holder_commitment_point.next_transaction_number() == 1 {
+		let both_sides_on_initial_commitment_number = msg.next_local_commitment_number == 1
+			&& INITIAL_COMMITMENT_NUMBER - self.holder_commitment_point.next_transaction_number() == 1;
+		let is_resuming_splice_negotiation = {
+			let their_next_funding_txid = msg
+				.next_funding
+				.as_ref()
+				.map(|next_funding| next_funding.txid);
+			let our_next_funding_txid = self
+				.context
+				.interactive_tx_signing_session
+				.as_ref()
+				.map(|signing_session| signing_session.unsigned_tx().compute_txid());
+			self.pending_splice.is_some() && their_next_funding_txid == our_next_funding_txid
+		};
+		let is_resuming_splice_locked = {
+			let their_splice_locked_txid = msg
+				.my_current_funding_locked
+				.as_ref()
+				.map(|funding_locked| funding_locked.txid);
+			let our_splice_locked_txid = self
+				.pending_splice
+				.as_ref()
+				.and_then(|pending_splice| pending_splice.sent_funding_txid)
+				.or(self.funding.get_funding_txid().filter(|_| {
+					self.funding
+						.channel_transaction_parameters
+						.splice_parent_funding_txid
+						.is_some()
+				}));
+			their_splice_locked_txid.is_some() && their_splice_locked_txid == our_splice_locked_txid
+		};
+		let channel_ready = if both_sides_on_initial_commitment_number
+			&& !is_resuming_splice_negotiation && !is_resuming_splice_locked
+		{
 			// We should never have to worry about MonitorUpdateInProgress resending ChannelReady
 			self.get_channel_ready(logger)
 		} else { None };