net: fec: quiesce packet processing when taking link down in fec_enet_adjust_link()

When the link goes down, the adjust_link method will be called, but
there is no synchronisation to ensure that we won't be processing some
last remaining packets via the NAPI handlers while performing a reset of
the device.

Add the necessary synchronisation to ensure that packet processing
is complete before we stop and reset the FEC.
Acked-by: Fugang Duan <B38611@freescale.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/fec_main.c

@@ -1530,7 +1530,11 @@ static void fec_enet_adjust_link(struct net_device *ndev)
 		}
 	} else {
 		if (fep->link) {
+			napi_disable(&fep->napi);
+			netif_tx_lock_bh(ndev);
 			fec_stop(ndev);
+			netif_tx_unlock_bh(ndev);
+			napi_enable(&fep->napi);
 			fep->link = phy_dev->link;
 			status_change = 1;
 		}