conf: simplify link from hostdev back to network device

conf: simplify link from hostdev back to network device

hostdevs have a link back to the original network device. This is fairly
generic accepting any type of device, however, we don't intend to make
use of this approach in future. It can thus be specialized to network
devices.

Reviewed-by: Cole Robinson <crobinso@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>