landlock: Document audit blocker field format

landlock: Document audit blocker field format

Add comprehensive documentation for the ``blockers`` field format
in AUDIT_LANDLOCK_ACCESS records, including all possible prefixes
(fs., net., scope.) and their meanings.

Also fix a typo and update the documentation date to reflect these
changes.

Signed-off-by: Samasth Norway Ananda <samasth.norway.ananda@oracle.com>
Link: https://lore.kernel.org/r/20260128031814.2945394-4-samasth.norway.ananda@oracle.com
Signed-off-by: Mickaël Salaün <mic@digikod.net>