LU-15200 llite: revalidate dentry if LOOKUP lock fetched

Once ll_inode_revalidate() fetches LOOKUP lock, it should revalidate
dentry, so subsequent lookup can find it in dcache.

It should also update lli_dir_depth.

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I847e16d64d605b91efc93925821bc29cbea20fa2
Reviewed-on: https://review.whamcloud.com/45599
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>