[netdrvr] remove manual driver poisoning of net_device

Such poisoning can cause oopses either because the refcount is not
zero when the poisoning occurs, or due to kernel debugging options
being enabled.

drivers/net/pci-skeleton.c

@@ -864,13 +864,6 @@ static void __devexit netdrv_remove_one (struct pci_dev *pdev)
 
 	pci_release_regions (pdev);
 
-#ifndef NETDRV_NDEBUG
-	/* poison memory before freeing */
-	memset (dev, 0xBC,
-		sizeof (struct net_device) +
-		sizeof (struct netdrv_private));
-#endif /* NETDRV_NDEBUG */
-
 	free_netdev (dev);
 
 	pci_set_drvdata (pdev, NULL);

drivers/net/r8169.c

@@ -642,10 +642,6 @@ rtl8169_remove_one(struct pci_dev *pdev)
 	iounmap(tp->mmio_addr);
 	pci_release_regions(pdev);
 
-	// poison memory before freeing 
-	memset(dev, 0xBC,
-	       sizeof (struct net_device) + sizeof (struct rtl8169_private));
-
 	pci_disable_device(pdev);
 	free_netdev(dev);
 	pci_set_drvdata(pdev, NULL);

drivers/net/sis190.c

@@ -703,10 +703,6 @@ SiS190_remove_one(struct pci_dev *pdev)
 	iounmap(tp->mmio_addr);
 	pci_release_regions(pdev);
 
-	// poison memory before freeing 
-	memset(dev, 0xBC,
-	       sizeof (struct net_device) + sizeof (struct sis190_private));
-
 	free_netdev(dev);
 	pci_set_drvdata(pdev, NULL);
 }