Fix unnecessary defined internal variable
Fix unnecessary defined internal variable

The variable filtered_ports is only used inside the try block,
and it is not necessarily to be defined as empty list first as the
following part will initialize it.

Change-Id: If90f6e86eeca5c060e6752d5ad9bd35f5d660382

openstack/kuryr,celebdor/kuryr-libnetwork,midonet/kuryr,celebdor/kuryr,midonet/kuryr,midonet/kuryr,celebdor/kuryr-libnetwork,celebdor/kuryr-libnetwork,openstack/kuryr,celebdor/kuryr