[feature request] Option to Ignore ULA

[dirdi]

It would be nice if there was an option (e.g. --noula) to exclude IPv6 unique local addresses (ULA, i.e. addresses starting with fc... or fd... ) from being selected by e.g. the default-ip plugin.

The reason behind this is that routers often assign ULAs additionally to an IPv6 address from the prefix assigned by the ISP. ddupdate then will sometimes pick the ULA instead of the globally routable IPv6 address.