message: rafs: fix the opendir() flag returned to kernel
  Otherwise the directory cache will be dropped on opening by kernel [1].
  Fixes:
  Reported-by: Daowen Luo
diff: @@ -910,7 +910,7 @@ impl FileSystem for Rafs {
  _flags: u32,
  ) -> Result<(Option<Self::Handle>, OpenOptions)> {
  // Cache dir since we are readonly
  - Ok((None, OpenOptions::CACHE_DIR))
  + Ok((None, OpenOptions::CACHE_DIR | OpenOptions::KEEP_CACHE))
  }
  fn releasedir(&self, _ctx: &Context, _inode: u64, _flags: u32, _handle: u64) -> Result<()> {
  