net: skip virtio-net config of deleted nic's peers

https://bugzilla.redhat.com/show_bug.cgi?id=1373816
qemu core dump happens during repetitive unpug-plug
with multiple queues and Windows RSS-capable guest.
If back-end delete requested during virtio-net device
initialization, driver still can try configure the device
for multiple queues. The virtio-net device is expected
to be removed as soon as the initialization is done.

Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
