linux-phytec-fsl

netfilter: ctnetlink: add const qualifier to nfnl_hook.get_ct

get_ct as is and will not update its skb argument, and users of
nfnl_ct_hook is currently only nfqueue, we can add const qualifier.

Signed-off-by: Ken-ichirou MATSUZAWA <chamas@h4.dion.ne.jp>