ipv4: Mark fib_combine_itag()'s 'res' arg as const.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index 08b46b8..b3019d8 100644
--- a/include/net/ip_fib.h
+++ b/include/net/ip_fib.h
@@ -232,7 +232,7 @@
 extern void fib_trie_init(void);
 extern struct fib_table *fib_trie_table(u32 id);
 
-static inline void fib_combine_itag(u32 *itag, struct fib_result *res)
+static inline void fib_combine_itag(u32 *itag, const struct fib_result *res)
 {
 #ifdef CONFIG_IP_ROUTE_CLASSID
 #ifdef CONFIG_IP_MULTIPLE_TABLES