LU-3285 mds: combine DoM bit with other IBITS

LU-3285 mds: combine DoM bit with other IBITS

The DoM bit combining with other ibits opens way to several
optimization, like getting IO lock in advance along with OPEN,
size attribute caching at client and others.

Test-Parameters: mdssizegb=20 testlist=sanity-dom,dom-performance
Signed-off-by: Mikhail Pershin <mike.pershin@intel.com>
Change-Id: I442f742b21efba84a0c61501f4877a36c7e9d572
Reviewed-on: https://review.whamcloud.com/28024
Tested-by: Jenkins
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>