Why does loopback timestampt then clear the timestamp for packets in xmit?

Question

The driver for the network interface "lo" (loopback device) for Linux does something that I do not understanding with its "outgoing" packets. See the related function:

static netdev_tx_t loopback_xmit(struct sk_buff *skb, struct net_device *dev)
{
    int len;

    skb_tx_timestamp(skb);

    /* do not fool net_timestamp_check() with various clock bases */
    skb_clear_tstamp(skb);

    skb_orphan(skb);

    /* Before queueing this packet to __netif_rx(),
     * make sure dst is refcounted.
     */
    skb_dst_force(skb);

    skb->protocol = eth_type_trans(skb, dev);

    len = skb->len;
    if (likely(__netif_rx(skb) == NET_RX_SUCCESS))
        dev_lstats_add(dev, len);

    return NETDEV_TX_OK;
}

I'm confused by these two lines specifically :

    skb_tx_timestamp(skb);
    skb_clear_tstamp(skb);

What would be the benefit of time stamping the packet just to immediately un-timestamping it?