smoketest: T4258: dhcp: bugfix failover ports
smoketest: T4258: dhcp: bugfix failover ports

Commit 5fc9ef9e ("DHCP : T4258: Set correct port for dhcp-failover") changed
how the failover port is rendered into the ISC DHCPd configuration - adjustment
of the smoketests was missed out.

vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x