multi: update to fn v2

lnrpc/routerrpc/forward_interceptor.go

@@ -3,7 +3,7 @@ package routerrpc
 import (
 	"errors"
 
-	"github.com/lightningnetwork/lnd/fn"
+	"github.com/lightningnetwork/lnd/fn/v2"
 	"github.com/lightningnetwork/lnd/graph/db/models"
 	"github.com/lightningnetwork/lnd/htlcswitch"
 	"github.com/lightningnetwork/lnd/lnrpc"