LU-12885 mds: add enums for MDS_OPEN flags (3/4)

LU-12885 mds: add enums for MDS_OPEN flags (3/4)

This patch is third of the series of patch that separates
kernel open flags from MDS open flags

This third step completes all of the MDS-side changes

This patch also changes/adds kernel-style doc instead
of old doxygen style wherever required

Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: I209ce38b49f9ee3c39b2ed8d16d231291cf5cdd1
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/56534
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>