netfiltr: ipt_CLUSTERIP: simplify seq_file codeA

Pass "struct clusterip_config" itself to seq_file iterators
and save one dereference. Proc entry itself isn't interesting.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>