LU-12885 llite: add enum ll_file_flags for clarity

LU-12885 llite: add enum ll_file_flags for clarity

Use enum ll_file_flags to store Lustre-internal flags on the open
file descriptor, instead of a generic "__u32 fd_flags", which can
easily be confused with any number of other flags in the code.

Rename variable "fd_flags" to "lfd_file_flags" to make this clear.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Idb4013610b9ef6f9461c8de275f6b5b4763ebbe5
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/45924
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Rajeev Mishra <rajeevm@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>