net: Init NAPI dev_list on napi_del

The recent GRO patches introduced the NAPI removal of devices in
free_netdev.  For drivers that can change the number of queues during
driver operation, the NAPI infrastructure doesn't allow the freeing and
re-addition of NAPI entities without reloading the driver.

This change reinitializes the dev_list in each NAPI struct on delete,
instead of just deleting it (and assigning the list pointers to POISON).
Drivers that wish to remove/re-add NAPI will need to re-initialize the
netdev napi_list after removing all NAPI instances, before re-adding NAPI
devices again.
Signed-off-by: NPeter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -2548,7 +2548,7 @@ void netif_napi_del(struct napi_struct *napi)
 {
 	struct sk_buff *skb, *next;
 
-	list_del(&napi->dev_list);
+	list_del_init(&napi->dev_list);
 
 	for (skb = napi->gro_list; skb; skb = next) {
 		next = skb->next;