Add IPv6 only host support

Adds support to add IPv6 only hosts,
It does this by rather then a gethostby lookup, we check if the user has entered an IP address rather than a hostname using inet_pton.
We don't need to know if the hostname is valid here, since the next check is a ping, which will fail if the hostname is incorrect.
Finally it adds a new dropdown to the addhost page, with a selection of tcp/udp/tcp6/udp6 with udp selected by default.