netfilter: arpt_mangle: fix return values of checkentry

netfilter: arpt_mangle: fix return values of checkentry

In 135367b "netfilter: xtables: change xt_target.checkentry return type",
the type returned by checkentry was changed from boolean to int, but the
return values where not adjusted.

arptables: Input/output error

This broke arptables with the mangle target since it returns true
under success, which is interpreted by xtables as >0, thus
returning EIO.

The following Linux kernels are affected:
* 2.6.35.9
* 2.6.36.4
* 2.6.37.3

Cc: stable@kernel.org
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
(cherry picked from commit 9d0db8b6b1da9e3d4c696ef29449700c58d589db)