selftests/landlock: Exhaustive test for the IOCTL allow-list

This test checks all IOCTL commands implemented in do_vfs_ioctl().

Test coverage for security/landlock is 90.9% of 722 lines according to
gcc/gcov-13.

Suggested-by: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Günther Noack <gnoack@google.com>
Link: https://lore.kernel.org/r/20240419161122.2023765-8-gnoack@google.com


[mic: Add test coverage]
Signed-off-by: Mickaël Salaün <mic@digikod.net>