IPv4: thresholds in fib_trie.c are not modified, make them const

Signed-off-by: Denis V. Lunev <den@openvz.org>
diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index 45a6e4d..57a2c46 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -299,10 +299,10 @@ static inline void check_tnode(const struct tnode *tn)
 	WARN_ON(tn && tn->pos+tn->bits > 32);
 }
 
-static int halve_threshold = 25;
-static int inflate_threshold = 50;
-static int halve_threshold_root = 15;
-static int inflate_threshold_root = 25;
+static const int halve_threshold = 25;
+static const int inflate_threshold = 50;
+static const int halve_threshold_root = 15;
+static const int inflate_threshold_root = 25;
 
 static void __alias_free_mem(struct rcu_head *head)
 {