l2tp: fix info leak in l2tp_ip6_recvmsg()

The L2TP code for IPv6 fails to initialize the l2tp_conn_id member of
struct sockaddr_l2tpip6 and therefore leaks four bytes kernel stack
in l2tp_ip6_recvmsg() in case msg_name is set.

Initialize l2tp_conn_id with 0 to avoid the info leak.

Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
static int __init l2tp_ip6_init(void)
{
	int err;

	pr_info("L2TP IP encapsulation support for IPv6 (L2TPv3)\n");

	err = proto_register(&l2tp_ip6_prot, 1);
	if (err != 0)
		goto out;

	err = inet6_add_protocol(&l2tp_ip6_protocol, IPPROTO_L2TP);
	if (err)
		goto out1;

	inet6_register_protosw(&l2tp_ip6_protosw);
	return 0;

out1:
	proto_unregister(&l2tp_ip6_prot);
out:
	return err;
}

static int __init l2tp_ip6_init(void)
{
	int err;

	pr_info("L2TP IP encapsulation support for IPv6 (L2TPv3)\n");

	err = proto_register(&l2tp_ip6_prot, 1);
	if (err != 0)
		goto out;

	err = inet6_add_protocol(&l2tp_ip6_protocol, IPPROTO_L2TP);
	if (err)
		goto out1;

	inet6_register_protosw(&l2tp_ip6_protosw);
	return 0;

out1:
	proto_unregister(&l2tp_ip6_prot);
out:
	return err;
}
