config: Experimental support for Litecoin/simnet

This PR adds the configuration needed to run LND with Litecoin on simnet. The change is minimal and has no impact for users that don't enable this mode. When using this configuration, the user is being warned that this mode is not officially supported.

config.go

@@ -541,10 +541,6 @@ func loadConfig() (*config, error) {
 			"litecoin.active must be set to 1 (true)", funcName)
 
 	case cfg.Litecoin.Active:
-		if cfg.Litecoin.SimNet {
-			str := "%s: simnet mode for litecoin not currently supported"
-			return nil, fmt.Errorf(str, funcName)
-		}
 		if cfg.Litecoin.RegTest {
 			str := "%s: regnet mode for litecoin not currently supported"
 			return nil, fmt.Errorf(str, funcName)
@@ -568,6 +564,10 @@ func loadConfig() (*config, error) {
 			numNets++
 			ltcParams = litecoinTestNetParams
 		}
+		if cfg.Litecoin.SimNet {
+			numNets++
+			ltcParams = litecoinSimNetParams
+		}
 		if numNets > 1 {
 			str := "%s: The mainnet, testnet, and simnet params " +
 				"can't be used together -- choose one of the " +