UPSTREAM: xtables: extend matches and targets with .usersize

In matches and targets that define a kernel-only tail to their
xt_match and xt_target data structs, add a field .usersize that
specifies up to where data is to be shared with userspace.

Performed a search for comment "Used internally by the kernel" to find
relevant matches and targets. Manually inspected the structs to derive
a valid offsetof.

Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

Bug: 120612905
Change-Id: I05372f848e14a2870ee6b3bdfa4cc6c42c5bc74c
(cherry picked from commit ec23189049651b16dc2ffab35a4371dc1f491aca)
Signed-off-by: Hridya Valsaraju <hridya@google.com>