record: stricter type for PaymentRelayInfo.BaseFee

In this commit, we update the PaymentRelayInfo struct's BaseFee member
to use a stricter type (lnwire.MilliSatoshi) instead of an ambigious
uint32.

htlcswitch/hop/iterator.go

@@ -465,11 +465,11 @@ func (b *BlindingKit) DecryptAndValidateFwdInfo(payload *Payload,
 // ceil(a/b) = (a + b - 1)/(b).
 //
 //nolint:lll,dupword
-func calculateForwardingAmount(incomingAmount lnwire.MilliSatoshi, baseFee,
+func calculateForwardingAmount(incomingAmount, baseFee lnwire.MilliSatoshi,
 	proportionalFee uint32) (lnwire.MilliSatoshi, error) {
 
 	// Sanity check to prevent overflow.
-	if incomingAmount < lnwire.MilliSatoshi(baseFee) {
+	if incomingAmount < baseFee {
 		return 0, fmt.Errorf("incoming amount: %v < base fee: %v",
 			incomingAmount, baseFee)
 	}

htlcswitch/hop/iterator_test.go

@@ -111,7 +111,7 @@ func TestForwardingAmountCalc(t *testing.T) {
 	tests := []struct {
 		name           string
 		incomingAmount lnwire.MilliSatoshi
-		baseFee        uint32
+		baseFee        lnwire.MilliSatoshi
 		proportional   uint32
 		forwardAmount  lnwire.MilliSatoshi
 		expectErr      bool