The hidden attribute was overridden by libc_hidden_proto on GNU/Linux.
It is incorrect because the function is used from nscd.
internal_function is not supposed to be used across DSO boundaries,
so this commit removes it (again, due to the use in nscd).
This commit fixes various aspects in the UDP client timeout handling.
Timeouts are now applied in a more consistent fashion. Discarded UDP
packets no longer prevent the timeout from happening at all.
