create_dhcp_reservation rewrote an existing reservation and called
service/reconfigure even when it already held exactly what was asked, e.g.
on a retried provisioning job. reconfigure stops and starts Kea (the Kea
service controller keeps reconfigureForceRestart() = true and configd has no
reload action), which once left a firewall without DHCP. A reservation whose
subnet, MAC (normalised), IP, hostname and description already match is now
left alone.
Refs NetOrk/netork#1187
Christian Manivong