netfilter: nf_conntrack_h323: lost .data_len definition for Q.931/ipv6

Could you please push this patch into stable@?
it fixes memory corruption in kernels  v3.5 .. v4.10

Lost .data_len definition leads to write beyond end of
struct nf_ct_h323_master. Usually it corrupts following
struct nf_conn_nat, however if nat is not loaded it corrupts
following slab object.

In mainline this problem went away in v4.11,
after commit 9f0f3ebeda47 ("netfilter: helpers: remove data_len usage
for inkernel helpers") however many stable kernels are still affected.

Fixes: 1afc5679 ("netfilter: nf_ct_helper: implement variable length helper private data") # v3.5
cc: stable@vger.kernel.org
Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

(cherry picked from commit 396ba2fc)