Drop non-anchor channel fee upper bound limit entirely

[TheBlueMatt]

Quite a while ago we added checks for the total current dust exposure on a channel to explicitly limit dust inflation attacks. When we did this, we kept the existing upper bound on the channel's feerate in place. However, these two things are redundant - the point of the feerate upper bound is to prevent dust inflation, and it does so in a crude way that can cause spurious force-closures.

Here we simply drop the upper bound entirely, relying on the dust inflation limit to prevent dust inflation instead.

[wpaulino]

When we did this, we kept the existing upper bound on the channel's feerate in place.

We kept it but increased it from 2x to 10x (see d3af49e). Do you recall why the bump was done then? I agree that it is redundant.

[TheBlueMatt]

I think we just didn't think it through at the time, or maybe as a sanity check?

[wpaulino]

LGTM but CI is failing

[TheBlueMatt]

Fixed.

[wpaulino]

The fuzz build failed now:

thread 'full_stack::tests::test_no_existing_test_breakage' panicked at 'assertion failed: `(left == right)`
  left: `None`,
 right: `Some(1)`', src/full_stack.rs:1040:9

[TheBlueMatt]

Grrrrr, fixed.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (b6f3d0a) 88.79% compared to head (d30d599) 89.83%.
Report is 33 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2696      +/-   ##
==========================================
+ Coverage   88.79%   89.83%   +1.04%     
==========================================
  Files         112      113       +1     
  Lines       88502    94464    +5962     
  Branches    88502    94464    +5962     
==========================================
+ Hits        78581    84862    +6281     
+ Misses       7690     7377     -313     
+ Partials     2231     2225       -6     

Files	Coverage Δ
lightning/src/chain/chaininterface.rs	97.14% <ø> (ø)
lightning/src/ln/channel.rs	93.62% <100.00%> (+5.22%)	⬆️
lightning/src/util/test_utils.rs	77.14% <100.00%> (-0.06%)	⬇️

... and 23 files with indirect coverage changes

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[TheBlueMatt]

Fix new warnings

$ git diff-tree -U1 40953beb d30d599a
diff --git a/lightning/src/ln/channel.rs b/lightning/src/ln/channel.rs
index 81a4cb9f4..3606b04e6 100644
--- a/lightning/src/ln/channel.rs
+++ b/lightning/src/ln/channel.rs
@@ -7669,3 +7669,3 @@ mod tests {
 	use crate::ln::channel::InitFeatures;
-	use crate::ln::channel::{Channel, ChannelState, InboundHTLCOutput, OutboundV1Channel, InboundV1Channel, OutboundHTLCOutput, InboundHTLCState, OutboundHTLCState, HTLCCandidate, HTLCInitiator, commit_tx_fee_msat};
+	use crate::ln::channel::{ChannelState, InboundHTLCOutput, OutboundV1Channel, InboundV1Channel, OutboundHTLCOutput, InboundHTLCState, OutboundHTLCState, HTLCCandidate, HTLCInitiator, commit_tx_fee_msat};
 	use crate::ln::channel::{MAX_FUNDING_SATOSHIS_NO_WUMBO, TOTAL_BITCOIN_SUPPLY_SATOSHIS, MIN_THEIR_CHAN_RESERVE_SATOSHIS};
diff --git a/lightning/src/util/test_utils.rs b/lightning/src/util/test_utils.rs
index 3ca26d529..337dfc063 100644
--- a/lightning/src/util/test_utils.rs
+++ b/lightning/src/util/test_utils.rs
@@ -96,3 +96,3 @@ pub struct TestFeeEstimator {
 impl chaininterface::FeeEstimator for TestFeeEstimator {
-	fn get_est_sat_per_1000_weight(&self, confirmation_target: ConfirmationTarget) -> u32 {
+	fn get_est_sat_per_1000_weight(&self, _confirmation_target: ConfirmationTarget) -> u32 {
 		*self.sat_per_kw.lock().unwrap()
$