icmp: icmp_send() can avoid a dev_put()

We can avoid touching device refcount in icmp_send(),
using dev_get_by_index_rcu()
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/icmp.c

@@ -501,15 +501,16 @@ void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info)
 	if (!(rt->rt_flags & RTCF_LOCAL)) {
 		struct net_device *dev = NULL;
 
+		rcu_read_lock();
 		if (rt->fl.iif &&
 			net->ipv4.sysctl_icmp_errors_use_inbound_ifaddr)
-			dev = dev_get_by_index(net, rt->fl.iif);
+			dev = dev_get_by_index_rcu(net, rt->fl.iif);
 
-		if (dev) {
+		if (dev)
 			saddr = inet_select_addr(dev, 0, RT_SCOPE_LINK);
-			dev_put(dev);
-		} else
+		else
 			saddr = 0;
+		rcu_read_unlock();
 	}
 
 	tos = icmp_pointers[type].error ? ((iph->tos & IPTOS_TOS_MASK) |