netfilter: x_tables: enforce nul-terminated table name from getsockopt GET_ENTRIES

netfilter: x_tables: enforce nul-terminated table name from getsockopt GET_ENTRIES

Orabug: 24690280
CVE: CVE-2016-3134

Make sure the table names via getsockopt GET_ENTRIES is nul-terminated
in ebtables and all the x_tables variants and their respective compat
code. Uncovered by KASAN.

Reported-by: Baozeng Ding <sploving1@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
(cherry picked from commit b301f2538759933cf9ff1f7c4f968da72e3f0757)
Signed-off-by: Brian Maly <brian.maly@oracle.com>