lnrpc: update grpc-gateway library to v2

rpcserver.go

@@ -28,7 +28,7 @@ import (
 	"github.com/btcsuite/btcwallet/waddrmgr"
 	"github.com/btcsuite/btcwallet/wallet/txauthor"
 	"github.com/davecgh/go-spew/spew"
-	proxy "github.com/grpc-ecosystem/grpc-gateway/runtime"
+	proxy "github.com/grpc-ecosystem/grpc-gateway/v2/runtime"
 	"github.com/lightningnetwork/lnd/autopilot"
 	"github.com/lightningnetwork/lnd/build"
 	"github.com/lightningnetwork/lnd/chainreg"
@@ -521,6 +521,11 @@ type rpcServer struct {
 	started  int32 // To be used atomically.
 	shutdown int32 // To be used atomically.
 
+	// Required by the grpc-gateway/v2 library for forward compatibility.
+	// Must be after the atomically used variables to not break struct
+	// alignment.
+	lnrpc.UnimplementedLightningServer
+
 	server *server
 
 	cfg *Config