selftests/bpf: add wrong type test to cgroup dev

Current cgroup_dev test mostly tests that device operation is accepted or
refused base on passed major/minor (and so, any operation performed during
test involves only char device)

Add a small subtest ensuring that the device type passed to bpf program
allows it to take decisions as well.

Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Signed-off-by: Alexis Lothoré (eBPF Foundation) <alexis.lothore@bootlin.com>
Link: https://lore.kernel.org/r/20240731-convert_dev_cgroup-v4-3-849425d90de6@bootlin.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

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

@@ -114,6 +114,10 @@ void test_cgroup_dev(void)
 	if (test__start_subtest("deny-write"))
 		test_write("/dev/zero", buf, TEST_BUFFER_SIZE, -1, EPERM);
 
+	if (test__start_subtest("deny-mknod-wrong-type"))
+		test_mknod("/dev/test_dev_cgroup_block", S_IFBLK, 1, 3, -1,
+			   EPERM);
+
 cleanup_progs:
 	dev_cgroup__destroy(skel);
 cleanup_cgroup: