linux: Disable io_uring

linux: Disable io_uring

This subsystem has been a frequent source of security vulnerabilities
affecting the Linux kernel; as a result, Google announced on June 14,
2023, that they would disable it in their environment as widely as
possible.

IPFire does not depend on the availability of io_uring. Therefore,
disable this subsystem as well in order to preemptively cut attack
surface.

See also: https://security.googleblog.com/2023/06/learnings-from-kctf-vrps-42-linux.html

Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>