Revert "net/mlx4_en: Fix panic during reboot"

This reverts commit 9d2afba058722d40cc02f430229c91611c0e8d16.

The original issue would possibly exist if an external module
tried calling our "ethtool_ops" without checking if it still
exists.

The right way of solving it is by simply doing the check in
the caller side.
Currently, no action is required as there's no such use case.

Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx4/en_netdev.c

@@ -2202,7 +2202,6 @@ void mlx4_en_destroy_netdev(struct net_device *dev)
 
 	if (!shutdown)
 		free_netdev(dev);
-	dev->ethtool_ops = NULL;
 }
 
 static int mlx4_en_change_mtu(struct net_device *dev, int new_mtu)