htlcswitch+invoices: log payment metadata

invoices/test_utils_test.go

@@ -30,6 +30,7 @@ type mockPayload struct {
 	mpp           *record.MPP
 	amp           *record.AMP
 	customRecords record.CustomSet
+	metadata      []byte
 }
 
 func (p *mockPayload) MultiPath() *record.MPP {
@@ -50,6 +51,10 @@ func (p *mockPayload) CustomRecords() record.CustomSet {
 	return p.customRecords
 }
 
+func (p *mockPayload) Metadata() []byte {
+	return p.metadata
+}
+
 const (
 	testHtlcExpiry = uint32(5)