Due to a possible NixOS bug, this commit has no effect on NixOS 20.09
where `RestrictAddressFamilies` is a no-op.
It's only relevant for NixOS unstable with cgroups v2.
bitcoind+zmq: instead of allowing all address families, only add the required
AF_NETLINK family.
lnd: lnd only runs a zmq client, not a server, therefore it requires
no additional address families.
lightning-pool, clightning-plugin-zmq: add AF_NETLINK.
Erik Arvstedt
Ian Shipman