vdpa/vdpa_sim_net: Report max device capabilities

Configure max supported virtqueues features on the management device.
This info can be retrieved using:

$ vdpa mgmtdev show
vdpasim_net:
  supported_classes net
  max_supported_vqs 2
  dev_features MAC ANY_LAYOUT VERSION_1 ACCESS_PLATFORM

Signed-off-by: Eli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20220105114646.577224-15-elic@nvidia.com


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>