ipv6: ip6_route_output does not modify sk parameter, so make it const

This avoids explicit cast to avoid 'discards qualifiers'
compiler warning in a netfilter patch that i've been working on.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ip6_route.h

@@ -70,7 +70,7 @@ static inline struct inet_peer *rt6_get_peer(struct rt6_info *rt)
 extern void			ip6_route_input(struct sk_buff *skb);
 
 extern struct dst_entry *	ip6_route_output(struct net *net,
-						 struct sock *sk,
+						 const struct sock *sk,
 						 struct flowi6 *fl6);
 
 extern int			ip6_route_init(void);

net/ipv6/route.c

@@ -854,7 +854,7 @@ static struct rt6_info *ip6_pol_route_output(struct net *net, struct fib6_table
 	return ip6_pol_route(net, table, fl6->flowi6_oif, fl6, flags);
 }
 
-struct dst_entry * ip6_route_output(struct net *net, struct sock *sk,
+struct dst_entry * ip6_route_output(struct net *net, const struct sock *sk,
 				    struct flowi6 *fl6)
 {
 	int flags = 0;