ipv6: ipv6_chk_prefix() rcu conversion

int ipv6_chk_prefix(const struct in6_addr *addr, struct net_device *dev)

{

	struct inet6_dev *idev;

	struct inet6_ifaddr *ifa;

	const struct inet6_ifaddr *ifa;

	const struct inet6_dev *idev;

	int	onlink;

	onlink = 0;

	rcu_read_lock();

	idev = __in6_dev_get(dev);

	if (idev) {

		read_lock_bh(&idev->lock);

		list_for_each_entry(ifa, &idev->addr_list, if_list) {

		list_for_each_entry_rcu(ifa, &idev->addr_list, if_list) {

			onlink = ipv6_prefix_equal(addr, &ifa->addr,

						   ifa->prefix_len);

			if (onlink)

				break;

		}

		read_unlock_bh(&idev->lock);

	}

	rcu_read_unlock();

	return onlink;