selftests/bpf: Test attaching bpf qdisc to mq and non root

Until we are certain that existing classful qdiscs work with bpf qdisc,
make sure we don't allow attaching a bpf qdisc to non root. Meanwhile,
attaching to mq is allowed.

Signed-off-by: Amery Hung <ameryhung@gmail.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://patch.msgid.link/20250409214606.2000194-11-ameryhung@gmail.com