net: switchdev: Fixed kerneldoc warning

Update kernel-doc line comments to fix warnings reported by make W=1.
net/switchdev/switchdev.c:413: warning: Function parameter or
member 'extack' not described in 'call_switchdev_notifiers'
Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Acked-by: Ivan Vecera <ivecera@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/switchdev/switchdev.c

@@ -404,7 +404,7 @@ EXPORT_SYMBOL_GPL(unregister_switchdev_notifier);
  *	@val: value passed unmodified to notifier function
  *	@dev: port device
  *	@info: notifier information data
- *
+ *	@extack: netlink extended ack
  *	Call all network notifier blocks.
  */
 int call_switchdev_notifiers(unsigned long val, struct net_device *dev,