netfilter: x_tables: introduce and use xt_copy_counters_from_user

netfilter: x_tables: introduce and use xt_copy_counters_from_user

Orabug: 24690280
CVE: CVE-2016-3134

[ Upstream commit d7591f0c41ce3e67600a982bab6989ef0f07b3ce ]

The three variants use same copy&pasted code, condense this into a
helper and use that.

Make sure info.name is 0-terminated.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
(cherry picked from commit b7aa372fec2c1d4a1fcf4398ae88ba94134b9522)
Signed-off-by: Brian Maly <brian.maly@oracle.com>