tools/bpf: fix bpf selftest test_cgroup_storage failure

The bpf selftest test_cgroup_storage failed in one of
our production test servers.
  # sudo ./test_cgroup_storage
  Failed to create map: Operation not permitted

It turns out this is due to insufficient locked memory
with system default 16KB.

Similar to other self tests, let us arm the process
with unlimited locked memory. With this change,
the test passed.
  # sudo ./test_cgroup_storage
  test_cgroup_storage:PASS

Fixes: 68cfa3ac ("selftests/bpf: add a cgroup storage test")
Cc: Roman Gushchin <guro@fb.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
Acked-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>