LU-12885 mds: add enums for MDS_OPEN flags (2/4)

LU-12885 mds: add enums for MDS_OPEN flags (2/4)

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

This second step changes och_flags to use MDS_* flags. This
also renames 'struct ll_file_data' variable from 'fd' to 'lfd'.
As 'fd' is generally used to denote kernel fd.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: I3b105da5930fde51a57b2cda7aef38cd1e1d774d
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/55066
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: jsimmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>