multi: make sure CPFP won't exceed max allowed fee rate

This commit updates the `fee()` method in `weightEstimator` to make sure
when doing CPFP we are not exceeding the max allowed fee rate. In order
to use the max fee rate, we need to modify several methods to pass the
configured value to the estimator.

sweep/tx_input_set.go

@@ -33,6 +33,9 @@ type txInputSetState struct {
 	// feeRate is the fee rate to use for the sweep transaction.
 	feeRate chainfee.SatPerKWeight
 
+	// maxFeeRate is the max allowed fee rate configured by the user.
+	maxFeeRate chainfee.SatPerKWeight
+
 	// inputTotal is the total value of all inputs.
 	inputTotal btcutil.Amount
 
@@ -61,7 +64,7 @@ type txInputSetState struct {
 // weightEstimate is the (worst case) tx weight with the current set of
 // inputs. It takes a parameter whether to add a change output or not.
 func (t *txInputSetState) weightEstimate(change bool) *weightEstimator {
-	weightEstimate := newWeightEstimator(t.feeRate)
+	weightEstimate := newWeightEstimator(t.feeRate, t.maxFeeRate)
 	for _, i := range t.inputs {
 		// Can ignore error, because it has already been checked when
 		// calculating the yields.
@@ -118,11 +121,12 @@ type txInputSet struct {
 }
 
 // newTxInputSet constructs a new, empty input set.
-func newTxInputSet(wallet Wallet, feePerKW chainfee.SatPerKWeight,
+func newTxInputSet(wallet Wallet, feePerKW, maxFeeRate chainfee.SatPerKWeight,
 	maxInputs int) *txInputSet {
 
 	state := txInputSetState{
-		feeRate: feePerKW,
+		feeRate:    feePerKW,
+		maxFeeRate: maxFeeRate,
 	}
 
 	b := txInputSet{