It adds a bit of latency (and is definitely not the best solution in
theory), but finally allows dropping IPv6 NAT and it works within the
constraits my home network has to live in.
This also changes the firewall rules for the IoT network to no longer
accept connections to ntp.org pool hosts over 123/UDP. All clients
should use the local NTP server.
This implements a crude mechanism for signalling my router to add the
packets to its own qdisc.
The way in which this is implemented with nftables is hacky because of
NixOS’ limitations on build-time checking (which obviously can’t know
about the existence of cgroups on the target).