Restrict use of SYSV message queues

[gnoack]

System V message queues are acquired with msgget(2).
The key for acquiring these is in a system-global namespace,
so it seems that we might want to restrict their use somehow,
even when they are rarely used in practice today, judging by Debian code search.

There are existing LSM hooks for these, called security_msg_queue_*.

Capsicum is also restricting System V IPC (https://www.usenix.org/legacy/event/sec10/tech/full_papers/Watson.pdf, page 4)

[l0kod]

Looks good! For IPCs, I think being able to scope them to Landlock domains would makes sense in most cases and be easy to use. I'm not sure it would be worth it to be able to create dedicated rules.

Anyway, that's really close to #7, #8, and #29.