message: rafs: add comment to RafsInode field  offset
  Thus to easy get acknowledged its ondisk size
diff: @@ -878,28 +878,26 @@ impl_bootstrap_converter!(OndiskInode);
  #[derive(Default, Clone, Copy, Debug)]
  pub struct OndiskChunkInfo {
  /// sha256(chunk), [char; RAFS_SHA256_LENGTH]
  - pub block_id: RafsDigest,
  + pub block_id: RafsDigest, // 32
  /// blob index (blob_id = blob_table[blob_index])
  pub blob_index: u32,
  /// chunk flags
  - pub flags: RafsChunkFlags,
  -
  + pub flags: RafsChunkFlags, // 40
  /// compressed size in blob
  pub compress_size: u32,
  /// decompressed size in blob
  - pub decompress_size: u32,
  + pub decompress_size: u32, // 48
  /// compressed offset in blob
  - pub compress_offset: u64,
  + pub compress_offset: u64, // 56
  /// decompressed offset in blob
  - pub decompress_offset: u64,
  -
  + pub decompress_offset: u64, // 64
  /// offset in file
  - pub file_offset: u64,
  + pub file_offset: u64, // 72
  /// chunk index, it's allocated sequentially
  /// starting from 0 for one blob.
  pub index: u32,
  /// reserved
  - pub reserved: u32,
  + pub reserved: u32, //80
  }
  impl OndiskChunkInfo {
  