vdpa_sim_net: Offer VIRTIO_NET_F_STATUS

VIRTIO_NET_S_LINK_UP is already returned in config reads since vdpasim
creation, but the feature bit was not offered to the driver.

Tested modifying VIRTIO_NET_S_LINK_UP and different values of "status"
in qemu virtio-net options, using vhost_vdpa.

Not considering as a fix, because there should be no driver trusting in
this config read before the feature flag.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Message-Id: <20221117155502.1394700-1-eperezma@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>