message: rafs/v6: implement Debug for Ondisk Inode trait
  Thus to print it out to debug
diff: @@ -475,6 +475,20 @@ pub trait RafsV6OndiskInode: RafsStore {
  fn nlink(&self) -> u32;
  }
  +impl Debug for &dyn RafsV6OndiskInode {
  + fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
  + f.debug_struct("Ondisk Inode")
  + .field("format", &self.format())
  + .field("ino", &self.ino())
  + .field("mode", &self.mode())
  + .field("size", &self.size())
  + .field("union", &self.union())
  + .field("nlink", &self.nlink())
  + .field("xattr count", &self.xattr_count())
  + .finish()
  + }
  +}
  +
  /// RAFS v6 inode on-disk format, 32 bytes.
  ///
  /// This structure is designed to be compatible with EROFS compact inode format.
  