Slightly increase the allowed fee upper limit on remote update_fees

At least lnd is fairly aggressively high in their (non-anchor) fee
estimation, running the risk of force-closure. Further, because we
rely on a fee estimator we don't have full control over, we should
not assume our users' fees are particularly conservative, and thus
give our peers a lot of leeway.

Author: TheBlueMatt

lightning/src/ln/channel.rs

@@ -669,7 +669,7 @@ impl<Signer: Sign> Channel<Signer> {
 		if feerate_per_kw < lower_limit {
 			return Err(ChannelError::Close(format!("Peer's feerate much too low. Actual: {}. Our expected lower limit: {}", feerate_per_kw, lower_limit)));
 		}
-		let upper_limit = fee_estimator.get_est_sat_per_1000_weight(ConfirmationTarget::HighPriority) as u64  * 2;
+		let upper_limit = fee_estimator.get_est_sat_per_1000_weight(ConfirmationTarget::HighPriority) as u64 * 4;
 		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)));
 		}