sockopt test that verifies chaining behavior.
v9:
* setsockopt chaining example
v7:
* rework the test to verify cgroup getsockopt chaining
Cc: Andrii Nakryiko <andriin@fb.com>
Cc: Martin Lau <kafai@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
