multi: cap anchors feerate at configurable maximum

This commit caps the update fee the initiator will send when the anchors
channel type is used. We do not limit anything on the receiver side.

10 sat/vbyte is the current default max fee rate we use. This should be
enough to ensure propagation before anchoring down the commitment
transaction.

peer/brontide.go

@@ -294,6 +294,10 @@ type Config struct {
 	// commitment fee. This only applies for the initiator of the channel.
 	MaxChannelFeeAllocation float64
 
+	// MaxAnchorsCommitFeeRate is the maximum fee rate we'll use as an
+	// initiator for anchor channel commitments.
+	MaxAnchorsCommitFeeRate chainfee.SatPerKWeight
+
 	// ServerPubKey is the serialized, compressed public key of our lnd node.
 	// It is used to determine which policy (channel edge) to pass to the
 	// ChannelLink.
@@ -815,6 +819,7 @@ func (p *Brontide) addLink(chanPoint *wire.OutPoint,
 		TowerClient:             towerClient,
 		MaxOutgoingCltvExpiry:   p.cfg.MaxOutgoingCltvExpiry,
 		MaxFeeAllocation:        p.cfg.MaxChannelFeeAllocation,
+		MaxAnchorsCommitFeeRate: p.cfg.MaxAnchorsCommitFeeRate,
 		NotifyActiveLink:        p.cfg.ChannelNotifier.NotifyActiveLinkEvent,
 		NotifyActiveChannel:     p.cfg.ChannelNotifier.NotifyActiveChannelEvent,
 		NotifyInactiveChannel:   p.cfg.ChannelNotifier.NotifyInactiveChannelEvent,