qdev/compat: virtio-net-pci 0.10 compatibility. Add vectors property, allowing to turn off msi by setting vectors=0. Add compat property to pc-0.10 disabling msi. Signed-off-by: Gerd Hoffmann <kraxel@redhat.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>