sfc: Rate-limit log message for PTP packets without a matching timestamp event

In case of a flood of PTP packets, the timestamp peripheral and MC
firmware on the SFN[56]322F boards may not be able to provide
timestamp events for all packets.  Don't complain too much about this.

Fixes: 7c236c43 ('sfc: Add support for IEEE-1588 PTP')
Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>

drivers/net/ethernet/sfc/ptp.c

@@ -717,8 +717,9 @@ static bool efx_ptp_process_events(struct efx_nic *efx, struct sk_buff_head *q)
 			__skb_queue_tail(q, skb);
 		} else if (time_after(jiffies, match->expiry)) {
 			match->state = PTP_PACKET_STATE_TIMED_OUT;
-			netif_warn(efx, rx_err, efx->net_dev,
-				   "PTP packet - no timestamp seen\n");
+			if (net_ratelimit())
+				netif_warn(efx, rx_err, efx->net_dev,
+					   "PTP packet - no timestamp seen\n");
 			__skb_queue_tail(q, skb);
 		} else {
 			/* Replace unprocessed entry and stop */