netfilter: ctnetlink: fix up for "netfilter: conntrack: remove unconfirmed list"

After merging the net-next tree, today's linux-next build (powerpc
ppc64_defconfig) produced this warning:

nf_conntrack_netlink.c:1717 warning: 'ctnetlink_dump_one_entry' defined but not used

Fixes: 8a75a2c1 ("netfilter: conntrack: remove unconfirmed list")
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Florian Westphal <fw@strlen.de>