Only send the OFFLINE hotplug event if be->netif is set. Firstly, this ensures

that OFFLINE is only sent if the ONLINE event has been sent.  Secondly, this
fixes one possible cause of the reopened bug #549 as it prevents be->netif
being dereferenced inside netback_uevent.  Early reports suggest that this is
not the only cause of #549, so that bug remains open for now.

Signed-off-by: Ewan Mellor <ewan@xensource.com>

linux-2.6-xen-sparse/drivers/xen/netback/xenbus.c

@@ -213,7 +213,8 @@ static void frontend_changed(struct xenbus_device *dev,
 		break;
 
 	case XenbusStateClosed:
-		kobject_uevent(&dev->dev.kobj, KOBJ_OFFLINE);
+		if (be->netif != NULL)
+			kobject_uevent(&dev->dev.kobj, KOBJ_OFFLINE);
 		device_unregister(&dev->dev);
 		break;