selftests/tc-testing: Create tests trying to add children to clsact/ingress qdiscs

selftests/tc-testing: Create tests trying to add children to clsact/ingress qdiscs

In response to Wang's bug report [1], add the following test cases:

- Try and fail to add an fq child to an ingress qdisc
- Try and fail to add an fq child to a clsact qdisc

[1] https://lore.kernel.org/netdev/20251105022213.1981982-1-wangliang74@huawei.com/

Reviewed-by: Pedro Tammela <pctammela@mojatatu.ai>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Reviewed-by: Cong Wang <cwang@multikernel.io>
Link: https://patch.msgid.link/20251106205621.3307639-2-victor@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>