selftests/tc-testing: Create tests to exercise act_ct binding restrictions

selftests/tc-testing: Create tests to exercise act_ct binding restrictions

Add 4 test cases to exercise new act_ct binding restrictions:

- Try to attach act_ct to an ets qdisc
- Attach act_ct to an ingress qdisc
- Attach act_ct to a clsact/egress qdisc
- Attach act_ct to a shared block

Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/20260225134349.1287037-2-victor@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>