selftests/bpf: Fix cgrp_local_storage on s390x

Sync the definition of socket_cookie between the eBPF program and the
test. Currently the test works by accident, since on little-endian it
is sometimes acceptable to access u64 as u32.

Signed-off-by: Ilya Leoshkevich <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

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

···
 
 struct socket_cookie {
 	__u64 cookie_key;
-	__u32 cookie_value;
+	__u64 cookie_value;
 };
 
 static void test_tp_btf(int cgroup_fd)