ipv4: remove ipv4_ifdown_dst from route.c

ipv4_ifdown_dst does nothing after IPv4 route caches removal,
so we can remove it.
Signed-off-by: NLi RongQing <roy.qing.li@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/route.c

@@ -139,11 +139,6 @@ static void		 ip_do_redirect(struct dst_entry *dst, struct sock *sk,
 					struct sk_buff *skb);
 static void		ipv4_dst_destroy(struct dst_entry *dst);
 
-static void ipv4_dst_ifdown(struct dst_entry *dst, struct net_device *dev,
-			    int how)
-{
-}
-
 static u32 *ipv4_cow_metrics(struct dst_entry *dst, unsigned long old)
 {
 	WARN_ON(1);
@@ -162,7 +157,6 @@ static struct dst_ops ipv4_dst_ops = {
 	.mtu =			ipv4_mtu,
 	.cow_metrics =		ipv4_cow_metrics,
 	.destroy =		ipv4_dst_destroy,
-	.ifdown =		ipv4_dst_ifdown,
 	.negative_advice =	ipv4_negative_advice,
 	.link_failure =		ipv4_link_failure,
 	.update_pmtu =		ip_rt_update_pmtu,