[NETFILTER]: ipt_CLUSTERIP: fix oops in checkentry function

The clusterip_config_find_get() already increases entries reference
counter, so there is no reason to do it twice in checkentry() callback.

This causes the config to be freed before it is removed from the list,
resulting in a crash when adding the next rule.

Signed-off-by: Jaroslav Kysela <perex@suse.cz>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>