selftests/bpf: Adapt cgroup effective query uapi change

The attach flags is meaningless for effective query and
its value will always be set as 0 during effective query.
Root cg's effective progs is always its attached progs,
so we use non-effective query to get its progs count and
attach flags. And we don't need the remain attach flags
check.

Fixes: b79c9fc9

 ("bpf: implement BPF_PROG_QUERY for BPF_LSM_CGROUP")
Signed-off-by: Pu Lehui <pulehui@huawei.com>
Link: https://lore.kernel.org/r/20220921104604.2340580-4-pulehui@huaweicloud.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>