Commit bc68244 ("dhcp-server: T2185: migrate from SysVinit to systemd") migrated
the DHCP subsystem to systemd, but on the test-system there was still the old
configuration file present not triggering this condition.
tftp-hpa which is the TFTP daemon used by VyOS does not support
listening on multiple IP adresses. With this limitation we will start
one TFTP daemon instance per configured listen-address via systemd.