multi: replace DefaultDustLimit with script-specific DustLimitForSize

This commit updates call-sites to use the proper dust limits for
various script types. This also updates the default dust limit used
in the funding flow to be 354 satoshis instead of 573 satoshis.

sweep/tx_input_set.go

@@ -7,7 +7,6 @@ import (
 	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/btcsuite/btcutil"
-	"github.com/btcsuite/btcwallet/wallet/txrules"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
@@ -109,9 +108,6 @@ func (t *txInputSetState) clone() txInputSetState {
 type txInputSet struct {
 	txInputSetState
 
-	// dustLimit is the minimum output value of the tx.
-	dustLimit btcutil.Amount
-
 	// maxInputs is the maximum number of inputs that will be accepted in
 	// the set.
 	maxInputs int
@@ -121,25 +117,15 @@ type txInputSet struct {
 	wallet Wallet
 }
 
-func dustLimit(relayFee chainfee.SatPerKWeight) btcutil.Amount {
-	return txrules.GetDustThreshold(
-		input.P2WPKHSize,
-		btcutil.Amount(relayFee.FeePerKVByte()),
-	)
-}
-
 // newTxInputSet constructs a new, empty input set.
-func newTxInputSet(wallet Wallet, feePerKW,
-	relayFee chainfee.SatPerKWeight, maxInputs int) *txInputSet {
-
-	dustLimit := dustLimit(relayFee)
+func newTxInputSet(wallet Wallet, feePerKW chainfee.SatPerKWeight,
+	maxInputs int) *txInputSet {
 
 	state := txInputSetState{
 		feeRate: feePerKW,
 	}
 
 	b := txInputSet{
-		dustLimit:       dustLimit,
 		maxInputs:       maxInputs,
 		wallet:          wallet,
 		txInputSetState: state,
@@ -153,7 +139,7 @@ func newTxInputSet(wallet Wallet, feePerKW,
 func (t *txInputSet) enoughInput() bool {
 	// If we have a change output above dust, then we certainly have enough
 	// inputs to the transaction.
-	if t.changeOutput >= t.dustLimit {
+	if t.changeOutput >= lnwallet.DustLimitForSize(input.P2WPKHSize) {
 		return true
 	}
 
@@ -192,8 +178,12 @@ func (t *txInputSet) addToState(inp input.Input, constraints addConstraints) *tx
 	// If the input comes with a required tx out that is below dust, we
 	// won't add it.
 	reqOut := inp.RequiredTxOut()
-	if reqOut != nil && btcutil.Amount(reqOut.Value) < t.dustLimit {
-		return nil
+	if reqOut != nil {
+		// Fetch the dust limit for this output.
+		dustLimit := lnwallet.DustLimitForSize(len(reqOut.PkScript))
+		if btcutil.Amount(reqOut.Value) < dustLimit {
+			return nil
+		}
 	}
 
 	// Clone the current set state.