LU-15850 mdt: pack default LMV in open reply

LU-15850 mdt: pack default LMV in open reply

Add flag MDS_OPEN_DEFAULT_LMV to indicate that default LMV should be
packed in open reply, otherwise if open fetches LOOKUP lock, client
won't know directory has default LMV, and in subdir creation default
LMV won't take effect.

Lustre-change: https://review.whamcloud.com/47576/
Lustre-commit: f6e4272fb0be5b798b7685bb40067e3f6877c8a5

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: If2300ca39f406169eff9eab8f973ca1c2bfc8202
Reviewed-on: https://review.whamcloud.com/47869
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>