Allow configuring different max fee rate from peer

We've run into issues a few times where channels will get force closed because CLN's fee estimator isn't as good as ours so the fee rate will be too high, resulting in a force close. It'd be nice if we'd have the ability to be able to increase this limit because generally this isn't malicious, just different views of the mempool.

Author: benthecarman

lightning/src/chain/chaininterface.rs

@@ -63,6 +63,10 @@ pub enum ConfirmationTarget {
 	Normal,
 	/// We'd like a transaction to confirm in the next few blocks.
 	HighPriority,
+	/// The maximum value we are willing to accept from our channel counterparties.
+	/// LDK will accept up to 25 sat/vByte or 10x our fee estimator's "High Priority" fee.
+	/// This can be used to further increase that limit.
+	Max,
 }
 
 /// A trait which should be implemented to provide feerate information on a number of time

lightning/src/ln/channel.rs

@@ -2157,8 +2157,9 @@ impl<SP: Deref> Channel<SP> where
 		if !channel_type.supports_anchors_zero_fee_htlc_tx() {
 			let upper_limit = cmp::max(250 * 25,
 				fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::HighPriority) as u64 * 10);
-			if feerate_per_kw as u64 > upper_limit {
-				return Err(ChannelError::Close(format!("Peer's feerate much too high. Actual: {}. Our expected upper limit: {}", feerate_per_kw, upper_limit)));
+			let user_upper_limit = cmp::max(upper_limit, fee_estimator.bounded_sat_per_1000_weight(ConfirmationTarget::Max) as u64);
+			if feerate_per_kw as u64 > user_upper_limit {
+				return Err(ChannelError::Close(format!("Peer's feerate much too high. Actual: {}. Our expected upper limit: {}", feerate_per_kw, user_upper_limit)));
 			}
 		}