virtio-net: Unlimit tx queue size if peer is vdpa

virtio-net: Unlimit tx queue size if peer is vdpa

The code used to limit the maximum size of tx queue for others backends
than vhost_user since the introduction of configurable tx queue size in
9b02e1618cf2 ("virtio-net: enable configurable tx queue size").

As vhost_user, vhost_vdpa devices should deal with memory region
crosses already, so let's use the full tx size.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Message-Id: <20220217175029.2517071-1-eperezma@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>