[NETFILTER]: Fix small information leak in SO_ORIGINAL_DST (CVE-2006-1343)

It appears that sockaddr_in.sin_zero is not zeroed during
getsockopt(...SO_ORIGINAL_DST...) operation. This can lead
to an information leak (CVE-2006-1343).

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>