change proto for getnameinfo()

arguments `hostlen' and `servlen' are `socklen_t' or `size_t' depending
the platform

- apple: I don't known, so I don't change the original definition (socklen_t)
- netbsd: socklen_t
- freebsd: size_t
- dragonfly: size_t
- openbsd: size_t
- bitrig: size_t