selftests: tc-testing: Add TDC tests that exercise reentrant enqueue behaviour

selftests: tc-testing: Add TDC tests that exercise reentrant enqueue behaviour

Add 5 TDC tests that exercise the reentrant enqueue behaviour in drr,
ets, qfq, and hfsc:

- Test DRR's enqueue reentrant behaviour with netem (which caused a
  double list add)
- Test ETS's enqueue reentrant behaviour with netem (which caused a double
  list add)
- Test QFQ's enqueue reentrant behaviour with netem (which caused a double
  list add)
- Test HFSC's enqueue reentrant behaviour with netem (which caused a UAF)
- Test nested DRR's enqueue reentrant behaviour with netem (which caused a
  double list add)

Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Link: https://patch.msgid.link/20250425220710.3964791-6-victor@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>