use getaddrinfo/getnameinfo to parse ipv6 addresses instead of

use getaddrinfo/getnameinfo to parse ipv6 addresses instead of
inet_pton/inet_ntop to allow specifing and printing the IPv6 scope
identifier. synced host_v6() with ntpd's version to use getaddrinfo()
instead of inet_pton() - host_v4, host_v6, and host_dns could all use
getaddrinfo in a single function by specifing different flags but this
would diverge from the other daemons using this common interface so we
keep this little overhead.

discussed with henning@
ok pyr@