xfrm: handle NETDEV_UNREGISTER for xfrm device

This patch to handle the asynchronous unregister
device event so the device IPsec offload resources
could be cleanly released.

Fixes: e4db5b61 ("xfrm: policy: remove pcpu policy cache")
Signed-off-by: Raed Salem <raeds@mellanox.com>
Reviewed-by: Boris Pismenny <borisp@mellanox.com>
Reviewed-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_device.c

@@ -383,6 +383,7 @@ static int xfrm_dev_event(struct notifier_block *this, unsigned long event, void
 		return xfrm_dev_feat_change(dev);
 
 	case NETDEV_DOWN:
+	case NETDEV_UNREGISTER:
 		return xfrm_dev_down(dev);
 	}
 	return NOTIFY_DONE;