netfilter: xt_connlimit: don't store address in the conn nodes

Only stored, never read.  This is a leftover from commit 7d084877


("netfilter: connlimit: use rbtree for per-host conntrack obj storage"),
which added the rbtree node struct that stores the address instead.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>