net: constify is_skb_forwardable's arguments

is_skb_forwardable is not supposed to change anything so constify its
arguments
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -3264,7 +3264,8 @@ struct sk_buff *dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
 				    struct netdev_queue *txq, int *ret);
 int __dev_forward_skb(struct net_device *dev, struct sk_buff *skb);
 int dev_forward_skb(struct net_device *dev, struct sk_buff *skb);
-bool is_skb_forwardable(struct net_device *dev, struct sk_buff *skb);
+bool is_skb_forwardable(const struct net_device *dev,
+			const struct sk_buff *skb);
 
 extern int		netdev_budget;
 

net/core/dev.c

@@ -1741,7 +1741,7 @@ static inline void net_timestamp_set(struct sk_buff *skb)
 			__net_timestamp(SKB);		\
 	}						\
 
-bool is_skb_forwardable(struct net_device *dev, struct sk_buff *skb)
+bool is_skb_forwardable(const struct net_device *dev, const struct sk_buff *skb)
 {
 	unsigned int len;