landlock: Log mount-related denials

landlock: Log mount-related denials

Add audit support for sb_mount, move_mount, sb_umount, sb_remount, and
sb_pivot_root hooks.

The new related blocker is "fs.change_topology".

Audit event sample:

  type=LANDLOCK_DENY msg=audit(1729738800.349:44): domain=195ba459b blockers=fs.change_topology name="/" dev="tmpfs" ino=1

Remove landlock_get_applicable_domain() and get_current_fs_domain()
which are now fully replaced with landlock_get_applicable_subject().

Cc: Günther Noack <gnoack@google.com>
Link: https://lore.kernel.org/r/20250320190717.2287696-12-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>