ipv4: remove nested rcu_read_lock/unlock

ip_local_deliver_finish() already have a rcu_read_lock/unlock, so
the rcu_read_lock/unlock is unnecessary.

See the stack below:
ip_local_deliver_finish
	|
	|
	->icmp_rcv
		|
		|
		->icmp_socket_deliver
Suggested-by: NHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: NDuan Jiong <duanj.fnst@cn.fujitsu.com>
Acked-by: NHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/icmp.c

@@ -670,11 +670,9 @@ static void icmp_socket_deliver(struct sk_buff *skb, u32 info)
 
 	raw_icmp_error(skb, protocol, info);
 
-	rcu_read_lock();
 	ipprot = rcu_dereference(inet_protos[protocol]);
 	if (ipprot && ipprot->err_handler)
 		ipprot->err_handler(skb, info);
-	rcu_read_unlock();
 }
 
 static bool icmp_tag_validation(int proto)