selftests/bpf: Make cgroup_v1v2 use its own port

This patch change cgroup_v1v2 use a different port, avoid conflict with
other tests.

Signed-off-by: Yucong Sun <sunyucong@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211006185619.364369-8-fallentree@fb.com