IPv6 support

[Arran Cudbard-Bell]

The server has IPv6 support in terms of it can send and receive RADIUS packets with IPv6, but lacks support in some modules which assumed NAS-IP-Address and Framed-IP-Address would always be IPv4.

Do people have a preference for the default SQL schemas whether fields like NAS-IP-Address are modified to take either an IPv4 or IPv6 or whether we use distinct fields? The same goes for Framed-IP-Address and Framed-IPv6-Prefix.

-Arran