Add support for IPv6 neighbors

[Giga-Pudding]

In case of dynamic IPv6 prefixes, every host on the network obtains it's own Global Unicast Address. But there might be devices on the network, that are not able to run this script on their own. Especially IoT devices, like Webcams or other "Smart" stuff, which cannot be accessed. So, how about extending this scripts functionality to also update AAAA records of other devices (IPv6 neighbors) on the same network? I see two ways to achieve this:

The easy way is by providing the Interface Identifier (last 64 bit of the IPv6 address) to the script manually. If you could specify a list of Interface Identifier and corresponding AAAA records, the script would have all what's needed to update other devices AAAA records as well, because the network prefix (first 64 bit) are the same for all hosts in this network/vlan. This method works fine, where the Interface Identifier is generated using the MAC address (EUI-64).

However, there are some network configurations where random IPv6 addresses are assigned by the DHCPv6 server. In that case, Neighbor Discovery Protocol could be used for a lookup of the full IPv6 address, after the address has changed.

What do you think?

[thcrt]

Somewhat related to #32.