[lbry] policy: relax dust thrashold to 1000 dewies/kB

An output is considered dust if the cost to the network to spend the
coins is more than 1/3 of the minimum free transaction relay fee, which
has a default rate of 1000 satoshis/kb

bitcoind refactored dust threshold calculation, which removed the
multiply factor of 3 from the code, but increased the DUST_RELAY_TX_FEE
from 1000 to 3000 (satoshi/kb).

lbrycrd adopted the refactored code but also kept the rate to
1000 dewies/kB, which means:

    An output is considered dust if the cost to the network to spend the
    coins is more than the minimum free transaction relay fee.

mempool/policy.go

@@ -249,7 +249,7 @@ func GetDustThreshold(txOut *wire.TxOut) int64 {
 		totalSize += 107
 	}
 
-	return 3 * int64(totalSize)
+	return int64(totalSize)
 }
 
 // IsDust returns whether or not the passed transaction output amount is
@@ -264,7 +264,7 @@ func IsDust(txOut *wire.TxOut, minRelayTxFee btcutil.Amount) bool {
 	}
 
 	// The output is considered dust if the cost to the network to spend the
-	// coins is more than 1/3 of the minimum free transaction relay fee.
+	// coins is more than the minimum free transaction relay fee.
 	// minFreeTxRelayFee is in Satoshi/KB, so multiply by 1000 to
 	// convert to bytes.
 	//
@@ -273,7 +273,7 @@ func IsDust(txOut *wire.TxOut, minRelayTxFee btcutil.Amount) bool {
 	// fee of 1000, this equates to values less than 546 satoshi being
 	// considered dust.
 	//
-	// The following is equivalent to (value/totalSize) * (1/3) * 1000
+	// The following is equivalent to (value/totalSize) * 1000
 	// without needing to do floating point math.
 	if txOut.Value > dustCap {
 		return false

mempool/policy_test.go

@@ -233,14 +233,14 @@ func TestDust(t *testing.T) {
 			true,
 		},
 		{
-			"38 byte public key script with value 584",
-			wire.TxOut{Value: 584, PkScript: pkScript},
+			"38 byte public key script with value 194",
+			wire.TxOut{Value: 194, PkScript: pkScript},
 			1000,
 			true,
 		},
 		{
-			"38 byte public key script with value 585",
-			wire.TxOut{Value: 585, PkScript: pkScript},
+			"38 byte public key script with value 195",
+			wire.TxOut{Value: 195, PkScript: pkScript},
 			1000,
 			false,
 		},