Merge branch 'move-sockopt-tests'

Stanislav Fomichev says:

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Now that test_progs is shaping into more generic test framework,
let's convert sockopt tests to it. This requires adding
a helper to create and join a cgroup first (test__join_cgroup).
Since we already hijack stdout/stderr that shouldn't be
a problem (cgroup helpers log to stderr).

The rest of the patches just move sockopt tests files under prog_tests/
and do the required small adjustments.
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Signed-off-by: Alexei Starovoitov <ast@kernel.org>