Avoid huge sockaddr_storage

Avoid huge sockaddr_storage

sockaddr_{in,in6} are enough and a simple sockaddr pointer is enough to
abstract them  (sockaddr_storage is what worked for me, there is no other
reason to use it).

While here, be portable and pass a non-zero length to getnameinfo(3);
while OpenBSD's implementation ignores it in the NI_NUMERICHOST case,
at least the old KAME stack didn't.

No functional change.

Prodded by florian
OK florian