netfilter: ipt_CLUSTERIP: remove "no conntrack!"

When a packet is meant to be handled by another node of the cluster,
silently drop it instead of flooding kernel log.

Note : INVALID packets are also dropped without notice.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>