Add some backend support for writing out a config so that the dhcp6 server can listen on the required MPD pppoe server interfaces.
Also nuke the failover entries, these don't exist for IPv6, this is handled by 2 servers and differing priorities
Update the GUI page for the DHCP6 server, add a if statement that prevents throwing range errors on interface that have no static IPv6 address.
It is entirely valid to operate a DHCP6 server just for prefix delegation, but ISC doesn't appear to allow it yet.