selftests/bpf: Convert sockopt_sk test to ASSERT_* macros

Convert the selftest to use the preferred ASSERT_* macros instead of the
deprecated CHECK().

Signed-off-by: Wang Yufen <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/testing/selftests/bpf/prog_tests/sockopt_sk.c

···
 	int cgroup_fd;
 
 	cgroup_fd = test__join_cgroup("/sockopt_sk");
-	if (CHECK_FAIL(cgroup_fd < 0))
+	if (!ASSERT_GE(cgroup_fd, 0, "join_cgroup /sockopt_sk"))
 		return;
 
 	run_test(cgroup_fd);