net/mlx5_vdpa: Offer VIRTIO_NET_F_MTU when setting MTU

Make sure to offer VIRTIO_NET_F_MTU since we configure the MTU based on
what was queried from the device.

This allows the virtio driver to allocate large enough buffers based on
the reported MTU.
Signed-off-by: NEli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20211124170949.51725-1-elic@nvidia.comSigned-off-by: NMichael S. Tsirkin <mst@redhat.com>
Acked-by: NJason Wang <jasowang@redhat.com>
Reviewed-by: NSi-Wei Liu <si-wei.liu@oracle.com>

drivers/vdpa/mlx5/net/mlx5_vnet.c

@@ -1895,6 +1895,7 @@ static u64 mlx5_vdpa_get_features(struct vdpa_device *vdev)
 	ndev->mvdev.mlx_features |= BIT_ULL(VIRTIO_NET_F_CTRL_MAC_ADDR);
 	ndev->mvdev.mlx_features |= BIT_ULL(VIRTIO_NET_F_MQ);
 	ndev->mvdev.mlx_features |= BIT_ULL(VIRTIO_NET_F_STATUS);
+	ndev->mvdev.mlx_features |= BIT_ULL(VIRTIO_NET_F_MTU);
 
 	print_features(mvdev, ndev->mvdev.mlx_features, false);
 	return ndev->mvdev.mlx_features;