af_packet: prevent information leak

In 2.6.27, commit 393e52e33c6c2 (packet: deliver VLAN TCI to userspace)
added a small information leak.

Add padding field and make sure its zeroed before copy to user.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
static void packet_dev_mclist(struct net_device *dev, struct packet_mclist *i, int what)
{
	for ( ; i; i = i->next) {
		if (i->ifindex == dev->ifindex)
			packet_dev_mc(dev, i, what);
	}
}

static void packet_dev_mclist(struct net_device *dev, struct packet_mclist *i, int what)
{
	for ( ; i; i = i->next) {
		if (i->ifindex == dev->ifindex)
			packet_dev_mc(dev, i, what);
	}
}
