Unregister the net device notifier before vhost exit

Unregister the net device notifier before going ahead and freeing
the memory that the vhost driver keeps. If the notifier is not
unregistered first, it can potentially access freed memory that
vhost driver maintains.

Change-Id: I2a51af25f591f0646876cc6f289df0eb03fc3655
Closes-BUG: #1561589

linux/vhost_dev.c

@@ -494,7 +494,7 @@ vhost_dellink(struct net_device *dev, struct list_head *head)
 
     vp = netdev_priv(dev);
     if (vp) {
-        if (vp->vp_db_index >= 0)
+        if (vhost_priv_db && vp->vp_db_index >= 0)
             vhost_priv_db[vp->vp_db_index] = NULL;
 
         vp->vp_db_index = -1;
@@ -566,8 +566,10 @@ void
 vhost_exit(void)
 {
     vhost_netlink_exit();
-    if (vhost_priv_db)
+    if (vhost_priv_db) {
         kfree(vhost_priv_db);
+        vhost_priv_db = NULL;
+    }
 
     return;
 }

linux/vr_host_interface.c

@@ -2339,8 +2339,8 @@ vr_host_vif_init(struct vrouter *router)
 void
 vr_host_interface_exit(void)
 {
-    vhost_exit();
     unregister_netdevice_notifier(&host_if_nb);
+    vhost_exit();
     linux_pkt_dev_free();
 
 #if (LINUX_VERSION_CODE < KERNEL_VERSION(2,6,39))