DPDK: fix crash at vifdump if there are no eth devices
DPDK: fix crash at vifdump if there are no eth devices

Add a check if DPDK port 0 exist before attach a KNI to it.

Change-Id: Ic40e32e9376cca3719d4a9daf0304ca3696d3e92
Closes-bug: #1538105

codilime/contrail-vrouter,codilime/contrail-vrouter,codilime/contrail-vrouter,codilime/contrail-vrouter