Resolve module does not currently track any state that has been set on
a per ifindex basis. This was okay while the set of information we
supported was quite small. However, with dhcpv6 support being prepared,
a more flexible framework is needed.
Change the resolve API to allocate and return an instance for a given
ifindex that has the ability to track information that was provided.
The module is responsible for the configuration of the address
resolution services. It will consist of the multiple service
specific plugins such as: systemd-resolved plugin, dnsmasq
plugin, etc.