qemu: init all queues to NO_VECTOR value

initialize vectors for all vqs to VIRTIO_NO_VECTOR rather than 0 which
is a valid vector. This fixes migration which happened before driver
was loaded.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reported-by: Amit Shah <amit.shah@redhat.com>
Tested-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
