net: phylink: don't call netif_carrier_off() with NULL netdev

Dan Carpenter points out that we have a code path that permits a NULL
netdev pointer to be passed to netif_carrier_off(), which will cause
a kernel oops. In any case, we need to set pl->old_link_state to false
to have the desired effect when there is no netdev present.

Fixes: f974936 ("net: phylink: add suspend/resume support")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/phylink.c

@@ -1333,7 +1333,10 @@ void phylink_suspend(struct phylink *pl, bool mac_wol)
 		 * but one would hope all packets have been sent. This
 		 * also means phylink_resolve() will do nothing.
 		 */
-		netif_carrier_off(pl->netdev);
+		if (pl->netdev)
+			netif_carrier_off(pl->netdev);
+		else
+			pl->old_link_state = false;
 
 		/* We do not call mac_link_down() here as we want the
 		 * link to remain up to receive the WoL packets.