landlock: Define access_mask_t to enforce a consistent access mask size

landlock: Define access_mask_t to enforce a consistent access mask size

BugLink: https://bugs.launchpad.net/bugs/1981864
commit 5f2ff33e10843ef51275c8611bdb7b49537aba5d upstream.

Create and use the access_mask_t typedef to enforce a consistent access
mask size and uniformly use a 16-bits type.  This will helps transition
to a 32-bits value one day.

Add a build check to make sure all (filesystem) access rights fit in.
This will be extended with a following commit.

Reviewed-by: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20220506161102.525323-2-mic@digikod.net
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>