We don't validate the backend queue numbers against bus limitation,
this will easily crash qemu if it exceeds the limitation which will
hit the abort() in virtio_del_queue(). An example is trying to
starting a virtio-net device with 256 queues. E.g:

./qemu-system-x86_64 -netdev tap,id=hn0,queues=256 -device
virtio-net-pci,netdev=hn0

Fixing this by doing the validation and fail early.

Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: qemu-stable <qemu-stable@nongnu.org>
Signed-off-by: NJason Wang <jasowang@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>