selftests/bpf: Add some tests with new bpf_program__attach_sockmap() APIs

Add a few more tests in sockmap_basic.c and sockmap_listen.c to
test bpf_link based APIs for SK_MSG and SK_SKB programs.
Link attach/detach/update are all tested.

All tests are passed.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20240410043547.3738448-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

selftests/bpf: Refactor out helper functions for a few tests

These helper functions will be used later new tests as well.
There are no functionality change.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20240410043542.3738166-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

bpf, selftests: Add sk_msg helpers load and attach test

The test itself is not particularly useful but it encodes a common
pattern we have.

Namely do a sk storage lookup then depending on data here decide if
we need to do more work or alternatively allow packet to PASS. Then
if we need to do more work consult task_struct for more information
about the running task. Finally based on this additional information
drop or pass the data. In this case the suspicious check is not so
realisitic but it encodes the general pattern and uses the helpers
so we test the workflow.

This is a load test to ensure verifier correctly handles this case.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/159033909665.12355.6166415847337547879.stgit@john-Precision-5820-Tower
Signed-off-by: Alexei Starovoitov <ast@kernel.org>