NETFILTER: arp_tables: fix userspace compilation

The included patch translates arpt_counters to xt_counters, making
userspace arptables compile against recent kernels.

Signed-off-by: Bart De Schuymer <bdschuym@pandora.be>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Adrian Bunk <bunk@stusta.de>