virtio-rng-pci: Allow setting nvectors, so we can use MSI-X

virtio-rng-pci: Allow setting nvectors, so we can use MSI-X

Most other virtio-pci devices allow MSI-X, let's have it for rng too.

Signed-off-by: David Daney <david.daney@fungible.com>
Reviewed-by: Marcin Nowakowski <marcin.nowakowski@fungible.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@fungible.com>
Message-Id: <20221014160947.66105-1-philmd@fungible.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>