net: delete redundant function declaration

The implement of function netdev_all_upper_get_next_dev_rcu has been
removed in:
	commit f1170fd4 ("net: Remove all_adj_list and its references")
so delete redundant declaration in header file.

Fixes: f1170fd4 ("net: Remove all_adj_list and its references")
Signed-off-by: Chen Wandun <chenwandun@huawei.com>
Link: https://lore.kernel.org/r/20211013094702.3931071-1-chenwandun@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/netdevice.h

@@ -4801,8 +4801,6 @@ struct netdev_nested_priv {
 bool netdev_has_upper_dev(struct net_device *dev, struct net_device *upper_dev);
 struct net_device *netdev_upper_get_next_dev_rcu(struct net_device *dev,
 						     struct list_head **iter);
-struct net_device *netdev_all_upper_get_next_dev_rcu(struct net_device *dev,
-						     struct list_head **iter);
 
 #ifdef CONFIG_LOCKDEP
 static LIST_HEAD(net_unlink_list);