efl_net_server_udp_client: make error easier to understand.

efl_net_server_udp_client: make error easier to understand.

UDP client has no socket on its own, so it can't be marked as
close-on-exec, however failing to resolve the method is bad as
confuses the user.

Instead provide a method that checks if the setting is different from
parent, in such case provide a meaningful message. Otherwise just be
quiet.