net: mscc: ocelot: warn when a PTP IRQ is raised for an unknown skb

When skb_match is NULL, it means we received a PTP IRQ for a timestamp
ID that the kernel has no idea about, since there is no skb in the
timestamping queue with that timestamp ID.

This is a grave error and not something to just "continue" over.
So print a big warning in case this happens.

Also, move the check above ocelot_get_hwtimestamp(), there is no point
in reading the full 64-bit current PTP time if we're not going to do
anything with it anyway for this skb.

Fixes: 4e3b0468 ("net: mscc: PTP Hardware Clock (PHC) support")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mscc/ocelot.c

@@ -747,12 +747,12 @@ void ocelot_get_txtstamp(struct ocelot *ocelot)
 
 		spin_unlock_irqrestore(&port->tx_skbs.lock, flags);
 
+		if (WARN_ON(!skb_match))
+			continue;
+
 		/* Get the h/w timestamp */
 		ocelot_get_hwtimestamp(ocelot, &ts);
 
-		if (unlikely(!skb_match))
-			continue;
-
 		/* Set the timestamp into the skb */
 		memset(&shhwtstamps, 0, sizeof(shhwtstamps));
 		shhwtstamps.hwtstamp = ktime_set(ts.tv_sec, ts.tv_nsec);