ipv4: fix counter in_slow_tot

since commit 89aef892("ipv4: Delete routing cache."), the counter
in_slow_tot can't work correctly.

The counter in_slow_tot increase by one when fib_lookup() return successfully
in ip_route_input_slow(), but actually the dst struct maybe not be created and
cached, so we can increase in_slow_tot after the dst struct is created.
Signed-off-by: NDuan Jiong <duanj.fnst@cn.fujitsu.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/route.c

@@ -1597,6 +1597,7 @@ static int __mkroute_input(struct sk_buff *skb,
 	rth->rt_gateway	= 0;
 	rth->rt_uses_gateway = 0;
 	INIT_LIST_HEAD(&rth->rt_uncached);
+	RT_CACHE_STAT_INC(in_slow_tot);
 
 	rth->dst.input = ip_forward;
 	rth->dst.output = ip_output;
@@ -1701,8 +1702,6 @@ static int ip_route_input_slow(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 		goto no_route;
 	}
 
-	RT_CACHE_STAT_INC(in_slow_tot);
-
 	if (res.type == RTN_BROADCAST)
 		goto brd_input;
 
@@ -1773,6 +1772,7 @@ out:	return err;
 	rth->rt_gateway	= 0;
 	rth->rt_uses_gateway = 0;
 	INIT_LIST_HEAD(&rth->rt_uncached);
+	RT_CACHE_STAT_INC(in_slow_tot);
 	if (res.type == RTN_UNREACHABLE) {
 		rth->dst.input= ip_error;
 		rth->dst.error= -err;