Merge branch 'move SYS() macro to test_progs.h and run mptcp in a dedicated netns'

Hangbin Liu says:

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As Martin suggested, let's move the SYS() macro to test_progs.h since
a lot of programs are using it. After that, let's run mptcp in a dedicated
netns to avoid user config influence.

v3: fix fd redirect typo. Move SYS() macro into the test_progs.h
v2: remove unneed close_cgroup_fd goto label.
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Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>