LU-13437 mdt: don't fetch LOOKUP lock for remote object

LU-13437 mdt: don't fetch LOOKUP lock for remote object

Pack parent FID in getattr by FID, which will be used to check whether
child is remote object on parent. The helper function is called
mdt_is_remote_object(). NB, directory shard is not treated as remote
object, because if so, client needs to revalidate shards when dir is
accessed, which will hurt performance much.

For getattr by FID, if object is remote file on parent, don't fetch
LOOKUP lock, otherwise client may see stale dir entries.

Lustre-change: https://review.whamcloud.com/38561
Lustre-commit: f9a2da63abab5b8b687842166a0b5b5e434ad441

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Yingjin Qian <qian@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Change-Id: I37b36983735eca63da37f190456b5cc1b861b29e
Reviewed-on: https://review.whamcloud.com/39769
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>