netfilter: xt_owner: Add supplementary groups option

netfilter: xt_owner: Add supplementary groups option

The XT_OWNER_SUPPL_GROUPS flag causes GIDs specified with XT_OWNER_GID
to be also checked in the supplementary groups of a process.

f_cred->group_info cannot be modified during its lifetime and f_cred
holds a reference to it so it's safe to use.

Signed-off-by: Lukasz Pawelczyk <l.pawelczyk@samsung.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
[sw0312.kim: backport from mainline to apply supplementary groups on netfilter]
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Change-Id: I7b56e3ca91f0632cb995cc1039a46a06717c77f3