mulit: don't set customData on the lnrpc route level

diff --git a/itest/lnd_forward_interceptor_test.go b/itest/lnd_forward_interceptor_test.go
index e8c1f41..8eec171 100644
--- a/itest/lnd_forward_interceptor_test.go
+++ b/itest/lnd_forward_interceptor_test.go
@@ -1,7 +1,6 @@
 package itest
 
 import (
-	"bytes"
 	"fmt"
 	"reflect"
 	"strings"
@@ -15,7 +14,6 @@ import (
 	"github.com/lightningnetwork/lnd/lntest/node"
 	"github.com/lightningnetwork/lnd/lntest/wait"
 	"github.com/lightningnetwork/lnd/lntypes"
-	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/routing/route"
 	"github.com/stretchr/testify/require"
 	"google.golang.org/grpc/codes"
@@ -477,17 +475,9 @@ func testForwardInterceptorRestart(ht *lntest.HarnessTest) {
 					rt.FirstHopAmountMsat)
 			}
 
-			cr := lnwire.CustomRecords(p.FirstHopCustomRecords)
-			recordData, err := cr.Serialize()
-			if err != nil {
-				return err
-			}
-
-			if !bytes.Equal(rt.CustomChannelData, recordData) {
-				return fmt.Errorf("expected custom records to "+
-					"be equal, got %x expected %x",
-					rt.CustomChannelData, recordData)
-			}
+			// Make sure the custom channel data is nil because
+			// this is not a custom channel payment.
+			require.Nil(ht, rt.CustomChannelData)
 
 			return nil
 		},
diff --git a/lnrpc/routerrpc/router_backend.go b/lnrpc/routerrpc/router_backend.go
index 377d0be..d19127f 100644
--- a/lnrpc/routerrpc/router_backend.go
+++ b/lnrpc/routerrpc/router_backend.go
@@ -1,6 +1,7 @@
 package routerrpc
 
 import (
+	"bytes"
 	"context"
 	"crypto/rand"
 	"encoding/hex"
@@ -622,10 +623,26 @@ func (r *RouterBackend) MarshallRoute(route *route.Route) (*lnrpc.Route, error)
 		// Allow the aux data parser to parse the custom records into
 		// a human-readable JSON (if available).
 		if r.ParseCustomChannelData != nil {
+			// Store the original custom data to check if parsing
+			// changed it.
+			originalCustomData := make([]byte, len(customData))
+			copy(originalCustomData, customData)
+
 			err := r.ParseCustomChannelData(resp)
 			if err != nil {
 				return nil, err
 			}
+
+			// We make sure we only set this field if the parser
+			// changed the data otherwise we might mistakenly
+			// show other tlv custom wire data as custom channel
+			// data.
+			if bytes.Equal(
+				originalCustomData, resp.CustomChannelData,
+			) {
+
+				resp.CustomChannelData = nil
+			}
 		}
 	}
 
diff --git a/payments/db/payment.go b/payments/db/payment.go
index f6d9983..9b7fe66 100644
--- a/payments/db/payment.go
+++ b/payments/db/payment.go
@@ -90,7 +90,8 @@ type PaymentCreationInfo struct {
 
 	// FirstHopCustomRecords are the TLV records that are to be sent to the
 	// first hop of this payment. These records will be transmitted via the
-	// wire message only and therefore do not affect the onion payload size.
+	// wire message (UpdateAddHTLC) only and therefore do not affect the
+	// onion payload size.
 	FirstHopCustomRecords lnwire.CustomRecords
 }
 
diff --git a/routing/route/route.go b/routing/route/route.go
index b3e91a6..349a2bc 100644
--- a/routing/route/route.go
+++ b/routing/route/route.go
@@ -524,9 +524,10 @@ type Route struct {
 	]
 
 	// FirstHopWireCustomRecords is a set of custom records that should be
-	// included in the wire message sent to the first hop. This is only set
-	// on custom channels and is used to include additional information
-	// about the actual value of the payment.
+	// included in the wire message sent to the first hop. This is for
+	// example used in custom channels. Besides custom channels we use it
+	// also for the endorsement bit. This data will be sent to the first
+	// hop in the UpdateAddHTLC message.
 	//
 	// NOTE: Since these records already represent TLV records, and we
 	// enforce them to be in the custom range (e.g. >= 65536), we don't use