sriov: stop virtual functions from being reported as nics

Previously we were reporting SR-IOV Virtual functions a regular nics.
This was misleading and was counter productive when wanting to use
a hook for attaching (or passing through) a VF as a vNIC to a VM.

This patch implements the first part, "Filter out unused virtual functions from
being reported as nics." of:
http://www.ovirt.org/Features/UCS_Integration

Change-Id: Idbb345ee22b7b108f1fd58765bd371339b82198f
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/22559
Reviewed-by: Dan Kenigsberg <danken@redhat.com>