multi: thread through the new max fee field for co-op close

In this commit, we parse the new max fee field, and pass it through the
switch, all the way to the peer where it's ultimately passed into the
chan closer state machine.

htlcswitch/switch.go

@@ -106,6 +106,12 @@ type ChanClose struct {
 	// process for the cooperative closure transaction kicks off.
 	TargetFeePerKw chainfee.SatPerKWeight
 
+	// MaxFee is the highest fee the caller is willing to pay.
+	//
+	// NOTE: This field is only respected if the caller is the initiator of
+	// the channel.
+	MaxFee chainfee.SatPerKWeight
+
 	// DeliveryScript is an optional delivery script to pay funds out to.
 	DeliveryScript lnwire.DeliveryAddress
 
@@ -1656,7 +1662,7 @@ func (s *Switch) teardownCircuit(pkt *htlcPacket) error {
 // optional parameter which sets a user specified script to close out to.
 func (s *Switch) CloseLink(chanPoint *wire.OutPoint,
 	closeType contractcourt.ChannelCloseType,
-	targetFeePerKw chainfee.SatPerKWeight,
+	targetFeePerKw, maxFee chainfee.SatPerKWeight,
 	deliveryScript lnwire.DeliveryAddress) (chan interface{}, chan error) {
 
 	// TODO(roasbeef) abstract out the close updates.
@@ -1668,6 +1674,7 @@ func (s *Switch) CloseLink(chanPoint *wire.OutPoint,
 		ChanPoint:      chanPoint,
 		Updates:        updateChan,
 		TargetFeePerKw: targetFeePerKw,
+		MaxFee:         maxFee,
 		DeliveryScript: deliveryScript,
 		Err:            errChan,
 	}