Send update_add_htlc messages after HTLC removal messages

While nodes are generally supposed to validate commitment
transactions after the `commitent_signed` and not while HTLCs are
being added/removed, we don't. This can make a commitment update
where we use HTLC balance claimed with a fulfill to send new HTLCs,
which is perfectly valid, being rejected. While we shouldn't
currently generate any such commitments, we might want to in the
future, and on the off-chance that we do, or where such a
commitment would result in a dust threshold overrun, its always
safter to add new HTLCs to a commitment only after we've removed
any HTLCs we're going to remove, which we do here.

Author: TheBlueMatt

lightning/src/ln/peer_handler.rs

@@ -3053,9 +3053,6 @@ where
 									commitment_signed.len(),
 									channel_id);
 							let mut peer = get_peer_for_forwarding!(node_id)?;
-							for msg in update_add_htlcs {
-								self.enqueue_message(&mut *peer, msg);
-							}
 							for msg in update_fulfill_htlcs {
 								self.enqueue_message(&mut *peer, msg);
 							}
@@ -3065,6 +3062,9 @@ where
 							for msg in update_fail_malformed_htlcs {
 								self.enqueue_message(&mut *peer, msg);
 							}
+							for msg in update_add_htlcs {
+								self.enqueue_message(&mut *peer, msg);
+							}
 							if let &Some(ref msg) = update_fee {
 								self.enqueue_message(&mut *peer, msg);
 							}