nfp: TX time stamp packets before HW doorbell is rung

commit 46f1c52e upstream.

TX completion may happen any time after HW queue was kicked.
We can't access the skb afterwards.  Move the time stamping
before ringing the doorbell.

Fixes: 4c352362 ("net: add driver for Netronome NFP4000/NFP6000 NIC VFs")
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/net/ethernet/netronome/nfp/nfp_net_common.c

@@ -854,6 +854,8 @@ static int nfp_net_tx(struct sk_buff *skb, struct net_device *netdev)
 
 	netdev_tx_sent_queue(nd_q, txbuf->real_len);
 
+	skb_tx_timestamp(skb);
+
 	tx_ring->wr_p += nr_frags + 1;
 	if (nfp_net_tx_ring_should_stop(tx_ring))
 		nfp_net_tx_ring_stop(nd_q, tx_ring);
@@ -866,8 +868,6 @@ static int nfp_net_tx(struct sk_buff *skb, struct net_device *netdev)
 		tx_ring->wr_ptr_add = 0;
 	}
 
-	skb_tx_timestamp(skb);
-
 	return NETDEV_TX_OK;
 
 err_unmap: