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.

chainreg/chainregistry.go

@@ -174,15 +174,6 @@ const (
 	BtcToLtcConversionRate = 60
 )
 
-// DefaultBtcChannelConstraints is the default set of channel constraints that are
-// meant to be used when initially funding a Bitcoin channel.
-//
-// TODO(halseth): make configurable at startup?
-var DefaultBtcChannelConstraints = channeldb.ChannelConstraints{
-	DustLimit:        lnwallet.DefaultDustLimit(),
-	MaxAcceptedHtlcs: input.MaxHTLCNumber / 2,
-}
-
 // DefaultLtcChannelConstraints is the default set of channel constraints that are
 // meant to be used when initially funding a Litecoin channel.
 var DefaultLtcChannelConstraints = channeldb.ChannelConstraints{
@@ -235,6 +226,19 @@ type ChainControl struct {
 	MinHtlcIn lnwire.MilliSatoshi
 }
 
+// GenDefaultBtcChannelConstraints generates the default set of channel
+// constraints that are to be used when funding a Bitcoin channel.
+func GenDefaultBtcConstraints() channeldb.ChannelConstraints {
+	// We use the dust limit for the maximally sized witness program with
+	// a 40-byte data push.
+	dustLimit := lnwallet.DustLimitForSize(input.UnknownWitnessSize)
+
+	return channeldb.ChannelConstraints{
+		DustLimit:        dustLimit,
+		MaxAcceptedHtlcs: input.MaxHTLCNumber / 2,
+	}
+}
+
 // NewChainControl attempts to create a ChainControl instance according
 // to the parameters in the passed configuration. Currently three
 // branches of ChainControl instances exist: one backed by a running btcd
@@ -674,7 +678,7 @@ func NewChainControl(cfg *Config, blockCache *blockcache.BlockCache) (
 	cc.Wc = wc
 
 	// Select the default channel constraints for the primary chain.
-	channelConstraints := DefaultBtcChannelConstraints
+	channelConstraints := GenDefaultBtcConstraints()
 	if cfg.PrimaryChain() == LitecoinChain {
 		channelConstraints = DefaultLtcChannelConstraints
 	}