switch hardlink id from int64 to bytes

other/java/client/src/main/proto/filer.proto

@@ -95,7 +95,7 @@ message Entry {
     repeated FileChunk chunks = 3;
     FuseAttributes attributes = 4;
     map<string, bytes> extended = 5;
-    int64 hard_link_id = 7;
+    bytes hard_link_id = 7;
     int32 hard_link_counter = 8; // only exists in hard link meta data
 }