xfrm: check for xdo_dev_ops add and delete

This adds a check for the required add and delete functions up front
at registration time to be sure both are defined.

Since both the features check and the registration check are looking
at the same things, break out the check for both to call.

Lastly, for some reason the feature check was setting xfrmdev_ops to
NULL if the NETIF_F_HW_ESP bit was missing, which would probably
surprise the driver later if the driver turned its NETIF_F_HW_ESP bit
back on.  We shouldn't be messing with the driver's callback list, so
we stop doing that with this patch.

Signed-off-by: Shannon Nelson <shannon.nelson@oracle.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_device.c

@@ -273,17 +273,31 @@ void xfrm_dev_backlog(struct softnet_data *sd)
 }
 #endif
 
-static int xfrm_dev_register(struct net_device *dev)
+static int xfrm_api_check(struct net_device *dev)
 {
-	if ((dev->features & NETIF_F_HW_ESP) && !dev->xfrmdev_ops)
-		return NOTIFY_BAD;
+#ifdef CONFIG_XFRM_OFFLOAD
 	if ((dev->features & NETIF_F_HW_ESP_TX_CSUM) &&
 	    !(dev->features & NETIF_F_HW_ESP))
 		return NOTIFY_BAD;
 
+	if ((dev->features & NETIF_F_HW_ESP) &&
+	    (!(dev->xfrmdev_ops &&
+	       dev->xfrmdev_ops->xdo_dev_state_add &&
+	       dev->xfrmdev_ops->xdo_dev_state_delete)))
+		return NOTIFY_BAD;
+#else
+	if (dev->features & (NETIF_F_HW_ESP | NETIF_F_HW_ESP_TX_CSUM))
+		return NOTIFY_BAD;
+#endif
+
 	return NOTIFY_DONE;
 }
 
+static int xfrm_dev_register(struct net_device *dev)
+{
+	return xfrm_api_check(dev);
+}
+
 static int xfrm_dev_unregister(struct net_device *dev)
 {
 	xfrm_policy_cache_flush();
@@ -292,16 +306,7 @@ static int xfrm_dev_unregister(struct net_device *dev)
 
 static int xfrm_dev_feat_change(struct net_device *dev)
 {
-	if ((dev->features & NETIF_F_HW_ESP) && !dev->xfrmdev_ops)
-		return NOTIFY_BAD;
-	else if (!(dev->features & NETIF_F_HW_ESP))
-		dev->xfrmdev_ops = NULL;
-
-	if ((dev->features & NETIF_F_HW_ESP_TX_CSUM) &&
-	    !(dev->features & NETIF_F_HW_ESP))
-		return NOTIFY_BAD;
-
-	return NOTIFY_DONE;
+	return xfrm_api_check(dev);
 }
 
 static int xfrm_dev_down(struct net_device *dev)