To avoid dnsmasq writing out the whole leasefile on each request
before replying. This gets slow on high‐latency storage.
Also tweak DNS updates a bit.
This reverts commit 554bf1f711.
Turns out ISC dhcrelay will relay even unicast packets from clients. So
the DHCP server got both the routed and the relayed query.
This tells dnsmasq to tell clients to send everything through the relay.
Since everything now comes from the relay we can drop access from client
networks.
Timotej Lazar