message: rafs/v6: implement is_hardlink() for v6 format
diff: @@ -878,7 +878,8 @@ impl RafsInode for OndiskInodeWrapper {
  /// Check whether the inode is a hardlink.
  fn is_hardlink(&self) -> bool {
  - todo!()
  + let inode = self.disk_inode();
  + inode.nlink() > 1 && self.is_reg()
  }
  /// Get inode number of the parent directory.
  