selftest/bpf: The test cases of BPF cookie for fentry/fexit/fmod_ret/lsm.

Make sure BPF cookies are correct for fentry/fexit/fmod_ret/lsm.

Signed-off-by: Kui-Feng Lee <kuifeng@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220510205923.3206889-6-kuifeng@fb.com