net: introduce netdev_change_features()

It will be needed by bonding and other drivers changing vlan_features
after ndo_init callback.

As a bonus, this includes kernel-doc for netdev_update_features().
Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -2565,6 +2565,7 @@ u32 netdev_increment_features(u32 all, u32 one, u32 mask);
 u32 netdev_fix_features(struct net_device *dev, u32 features);
 int __netdev_update_features(struct net_device *dev);
 void netdev_update_features(struct net_device *dev);
+void netdev_change_features(struct net_device *dev);
 
 void netif_stacked_transfer_operstate(const struct net_device *rootdev,
 					struct net_device *dev);

net/core/dev.c

@@ -5289,6 +5289,14 @@ int __netdev_update_features(struct net_device *dev)
 	return 1;
 }
 
+/**
+ *	netdev_update_features - recalculate device features
+ *	@dev: the device to check
+ *
+ *	Recalculate dev->features set and send notifications if it
+ *	has changed. Should be called after driver or hardware dependent
+ *	conditions might have changed that influence the features.
+ */
 void netdev_update_features(struct net_device *dev)
 {
 	if (__netdev_update_features(dev))
@@ -5296,6 +5304,23 @@ void netdev_update_features(struct net_device *dev)
 }
 EXPORT_SYMBOL(netdev_update_features);
 
+/**
+ *	netdev_change_features - recalculate device features
+ *	@dev: the device to check
+ *
+ *	Recalculate dev->features set and send notifications even
+ *	if they have not changed. Should be called instead of
+ *	netdev_update_features() if also dev->vlan_features might
+ *	have changed to allow the changes to be propagated to stacked
+ *	VLAN devices.
+ */
+void netdev_change_features(struct net_device *dev)
+{
+	__netdev_update_features(dev);
+	netdev_features_change(dev);
+}
+EXPORT_SYMBOL(netdev_change_features);
+
 /**
  *	netif_stacked_transfer_operstate -	transfer operstate
  *	@rootdev: the root or lower level device to transfer state from