[NFNETLINK_QUEUE] nfqueue message is on a diet

Fix oversized message, use NLMSG_SPACE just one since it reserves space
for the netlink header.

Sign-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

-- 
The dawn of the fourth age of Linux firewalling is coming; a time of
great struggle and heroic deeds -- J.Kadlecsik got inspired by J.Morris