lnd+rpc: define external subserver config only once

We don't have to define the external subserver config more than once, so
it is not needed to be defined for every listener. Instead we move it to
the ListenerConfig.

lnd.go

@@ -163,14 +163,6 @@ type ListenerWithSignal struct {
 
 	// Ready will be closed by the server listening on Listener.
 	Ready chan struct{}
-
-	// ExternalRPCSubserverCfg is optional and specifies the registration
-	// callback and permissions to register external gRPC subservers.
-	ExternalRPCSubserverCfg *RPCSubserverConfig
-
-	// ExternalRestRegistrar is optional and specifies the registration
-	// callback to register external REST subservers.
-	ExternalRestRegistrar RestRegistrar
 }
 
 // ListenerCfg is a wrapper around custom listeners that can be passed to lnd
@@ -183,6 +175,14 @@ type ListenerCfg struct {
 	// RPCListener can be set to the listener to use for the RPC server. If
 	// nil a regular network listener will be created.
 	RPCListener *ListenerWithSignal
+
+	// ExternalRPCSubserverCfg is optional and specifies the registration
+	// callback and permissions to register external gRPC subservers.
+	ExternalRPCSubserverCfg *RPCSubserverConfig
+
+	// ExternalRestRegistrar is optional and specifies the registration
+	// callback to register external REST subservers.
+	ExternalRestRegistrar RestRegistrar
 }
 
 // rpcListeners is a function type used for closures that fetches a set of RPC
@@ -752,7 +752,8 @@ func Main(cfg *Config, lisCfg ListenerCfg, shutdownChan <-chan struct{}) error {
 		cfg, server, macaroonService, cfg.SubRPCServers, serverOpts,
 		restDialOpts, restProxyDest, atplManager, server.invoices,
 		tower, restListen, rpcListeners, chainedAcceptor,
-		interceptorChain,
+		interceptorChain, lisCfg.ExternalRPCSubserverCfg,
+		lisCfg.ExternalRestRegistrar,
 	)
 	if err != nil {
 		err := fmt.Errorf("unable to create RPC server: %v", err)