netrom: fix info leak via msg_name in nr_recvmsg()

In case msg_name is set the sockaddr info gets filled out, as
requested, but the code fails to initialize the padding bytes of
struct sockaddr_ax25 inserted by the compiler for alignment. Also
the sax25_ndigis member does not get assigned, leaking four more
bytes.

Both issues lead to the fact that the code will leak uninitialized
kernel stack bytes in net/socket.c.

Fix both issues by initializing the memory with memset(0).

Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
static int nr_device_event(struct notifier_block *this, unsigned long event, void *ptr)
{
	struct net_device *dev = (struct net_device *)ptr;

	if (!net_eq(dev_net(dev), &init_net))
		return NOTIFY_DONE;

	if (event != NETDEV_DOWN)
		return NOTIFY_DONE;

	nr_kill_by_device(dev);
	nr_rt_device_down(dev);

	return NOTIFY_DONE;
}

static int nr_device_event(struct notifier_block *this, unsigned long event, void *ptr)
{
	struct net_device *dev = (struct net_device *)ptr;

	if (!net_eq(dev_net(dev), &init_net))
		return NOTIFY_DONE;

	if (event != NETDEV_DOWN)
		return NOTIFY_DONE;

	nr_kill_by_device(dev);
	nr_rt_device_down(dev);

	return NOTIFY_DONE;
}
