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>