bpf, selftests: Add various BPF tc link selftests

Add a big batch of selftest to extend test_progs with various tc link,
attach ops and old-style tc BPF attachments via libbpf APIs. Also test
multi-program attachments including mixing the various attach options:

  # ./test_progs -t tc_link
  torvalds#179     tc_link_base:OK
  torvalds#180     tc_link_detach:OK
  torvalds#181     tc_link_mix:OK
  torvalds#182     tc_link_opts:OK
  torvalds#183     tc_link_run_base:OK
  torvalds#184     tc_link_run_chain:OK
  Summary: 6/0 PASSED, 0 SKIPPED, 0 FAILED

All new and existing test cases pass.

Co-developed-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: Nikolay Aleksandrov <razor@blackwall.org>
Co-developed-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>