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.

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: Id181ecc053579ee394080381a82706334503ced0
Reviewed-on: https://review.whamcloud.com/38561


Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Yingjin Qian <qian@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>