Enable build scripts for IPv6

[opennetadmin]

need to output IPv6 compatible dhcp configurations. As long as your are on a newer version of ISC dhcp (4+ maybe older even) it should handle both v6 and v4.

It should be as simple as detecting if IP is v6.. then add 6 to the following key words:

subnet6
range6
fixed-address6

Of course you would be outputting appropriately formatted IP address values as well. Need to ensure all the functions and queries would handle things correctly.

Also watch out for periphery options and settings that may contain v6 addresses. Make sure they work correctly.