LU-6528 mdt: keep FS capability for intent_getattr

LU-6528 mdt: keep FS capability for intent_getattr

When "no_subtree_check" is set for NFS export, nfsd_set_fh_dentry()
doesn't set correct fsuid explicitely, but raise capability to allow
exportfs_decode_fh() to reconnect disconnected dentry into dcache.
So for lookup (i.e. intent_getattr), we should keep FS capability on
MDS, otherwise it will fail permission check.

Signed-off-by: Lai Siyao <lai.siyao@intel.com>
Change-Id: I99e2caeec06239a1df39918cbd6e9213e37ec758
Reviewed-on: http://review.whamcloud.com/14978
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>