bpf/selftests: Check errno when percpu map value size exceeds

This test case checks the errno message when percpu map value size
exceeds PCPU_MIN_UNIT_SIZE.

root@debian:~# ./test_maps
...
test_map_percpu_stats_hash_of_maps:PASS
test_map_percpu_stats_map_value_size:PASS
test_sk_storage_map:PASS

Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Tao Chen <chen.dylane@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240910144111.1464912-3-chen.dylane@gmail.com