Fix broken port query in Extraroute test case

One of the queries in an extra route test case tries
to filter based on the port owner, but the _list_ports
method it calls doesn't take a device_owner parameter.
This can cause failures if a DHCP port is created on
the same subnet.

Change-Id: I0e62027ae4d98944ef91a5d457d43d4224441b2f
Merge "Fix broken port query in Extraroute test case"