walletrpc: export wallet kit sub server name

We'll want to re-use the PSBT funding functionality from the wallet kit
sub server in the main RPC server. To be able to dynamically obtain an
instance of the wallet kit server we need to know its name under which
it registers itself in the list of sub server. We export the name so we
don't have to hard code it in the main server.

lnrpc/walletrpc/driver.go

@@ -16,13 +16,13 @@ func createNewSubServer(configRegistry lnrpc.SubServerConfigDispatcher) (
 	*WalletKit, lnrpc.MacaroonPerms, error) {
 
 	// We'll attempt to look up the config that we expect, according to our
-	// subServerName name. If we can't find this, then we'll exit with an
+	// SubServerName name. If we can't find this, then we'll exit with an
 	// error, as we're unable to properly initialize ourselves without this
 	// config.
-	walletKitServerConf, ok := configRegistry.FetchConfig(subServerName)
+	walletKitServerConf, ok := configRegistry.FetchConfig(SubServerName)
 	if !ok {
 		return nil, nil, fmt.Errorf("unable to find config for "+
-			"subserver type %s", subServerName)
+			"subserver type %s", SubServerName)
 	}
 
 	// Now that we've found an object mapping to our service name, we'll
@@ -30,7 +30,7 @@ func createNewSubServer(configRegistry lnrpc.SubServerConfigDispatcher) (
 	config, ok := walletKitServerConf.(*Config)
 	if !ok {
 		return nil, nil, fmt.Errorf("wrong type of config for "+
-			"subserver %s, expected %T got %T", subServerName,
+			"subserver %s, expected %T got %T", SubServerName,
 			&Config{}, walletKitServerConf)
 	}
 
@@ -68,7 +68,7 @@ func createNewSubServer(configRegistry lnrpc.SubServerConfigDispatcher) (
 
 func init() {
 	subServer := &lnrpc.SubServerDriver{
-		SubServerName: subServerName,
+		SubServerName: SubServerName,
 		NewGrpcHandler: func() lnrpc.GrpcHandler {
 			return &ServerShell{}
 		},
@@ -78,6 +78,6 @@ func init() {
 	// sub-RPC server within the global lnrpc package namespace.
 	if err := lnrpc.RegisterSubServer(subServer); err != nil {
 		panic(fmt.Sprintf("failed to register sub server driver '%s': %v",
-			subServerName, err))
+			SubServerName, err))
 	}
 }