y2038: inet: Convert inet deadline to support 64 bit time

This change brings 64 bit time support to inet deadline related code for
architectures with __WORDSIZE == 32 && __TIMESIZE != 64.

It is also safe to replace struct timespec with struct __timespec64 in
deadline related structures as:

- The __deadline_to_ms () returns the number of miliseconds to deadline to
  be used with __poll (and hence it is a relative value).
- To calculate the deadline from timeval (which will be converted latter)
  the uintmax_t type is used (unsinged long long int).

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>