l2tp: fix info leak via getsockname()

l2tp: fix info leak via getsockname()

[ Upstream commit 04d4fbca1017c11381e7d82acea21dd741e748bc ]

The L2TP code for IPv6 fails to initialize the l2tp_unused member of
struct sockaddr_l2tpip6 and that for leaks two bytes kernel stack via
the getsockname() syscall. Initialize l2tp_unused with 0 to avoid the
info leak.

Signed-off-by: Mathias Krause <minipli@googlemail.com>
Cc: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>