LU-14734 osd-ldiskfs: enable large_dir automatically

LU-14734 osd-ldiskfs: enable large_dir automatically

Enable the large_dir feature automatically at mount time for
filesystems that do not have it enabled already.  Otherwise,
the REMOTE_PARENT_DIR may overflow if there are many remote
entries created, or for object directories on very large OSTs.
It isn't really needed on a dedicated MGS filesystem.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I1c4ead26b09d60567ad12945d7b366b53475cebb
Reviewed-on: https://review.whamcloud.com/43931
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>