qemu: fix hotplug for multiqueue vdpa net device

qemu: fix hotplug for multiqueue vdpa net device

While commit a5e659f0 removed the restriction against multiple queues
for the vdpa net device, there were some missing pieces. Configuring a
device statically and then starting the domain worked as expected, but
hotplugging a device didn't have the expected multiqueue support
enabled. Add the missing bits.

Consider the following device xml:
    <interface type="vdpa">
      <mac address="00:11:22:33:44:03" />
      <source dev="/dev/vhost-vdpa-0" />
      <model type="virtio" />
      <driver queues='2' />
    </interface>

Without this patch, hotplugging the above XML description resulted in
the following:
    {"execute":"netdev_add","arguments":{"type":"vhost-vdpa","vhostdev":"/dev/fdset/0","id":"hostnet1"},"id":"libvirt-392"}
    {"execute":"device_add","arguments":{"driver":"virtio-net-pci","netdev":"hostnet1","id":"net1","mac":"00:11:22:33:44:03","bus":"pci.5","addr":"0x0"},"id":"libvirt-393"}

With the patch, hotplugging results in the following:
    {"execute":"netdev_add","arguments":{"type":"vhost-vdpa","vhostdev":"/dev/fdset/0","queues":2,"id":"hostnet1"},"id":"libvirt-392"}
    {"execute":"device_add","arguments":{"driver":"virtio-net-pci","mq":true,"vectors":6,"netdev":"hostnet1","id":"net1","mac":"00:11:22:33:44:03","bus":"pci.5","addr":"0x0"},"id":"libvirt-393"}

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2024406

Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>