multi: add reset closure to kvdb.Update

Similarly as with kvdb.View this commits adds a reset closure to the
kvdb.Update call in order to be able to reset external state if the
underlying db backend needs to retry the transaction.

htlcswitch/payment_result.go

@@ -305,5 +305,5 @@ func (store *networkResultStore) cleanStore(keep map[uint64]struct{}) error {
 		}
 
 		return nil
-	})
+	}, func() {})
 }