netfilter: arpt_mangle: fix return values of checkentry

In 135367b8 "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.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>

net/ipv4/netfilter/arpt_mangle.c

@@ -60,12 +60,12 @@ static int checkentry(const struct xt_tgchk_param *par)
 
 	if (mangle->flags & ~ARPT_MANGLE_MASK ||
 	    !(mangle->flags & ARPT_MANGLE_MASK))
-		return false;
+		return -EINVAL;
 
 	if (mangle->target != NF_DROP && mangle->target != NF_ACCEPT &&
 	   mangle->target != XT_CONTINUE)
-		return false;
-	return true;
+		return -EINVAL;
+	return 0;
 }
 
 static struct xt_target arpt_mangle_reg __read_mostly = {