netfilter: xtables: change targets to return error code

Part of the transition of done by this semantic patch:
// <smpl>
@ rule1 @
struct xt_target ops;
identifier check;
@@
 ops.checkentry = check;

@@
identifier rule1.check;
@@
 check(...) { <...
-return true;
+return 0;
 ...> }

@@
identifier rule1.check;
@@
 check(...) { <...
-return false;
+return -EINVAL;
 ...> }
// </smpl>

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/net/ipv4/netfilter/ipt_ECN.c b/net/ipv4/netfilter/ipt_ECN.c
index 9d96500..563049f 100644
--- a/net/ipv4/netfilter/ipt_ECN.c
+++ b/net/ipv4/netfilter/ipt_ECN.c
@@ -100,18 +100,18 @@
 
 	if (einfo->operation & IPT_ECN_OP_MASK) {
 		pr_info("unsupported ECN operation %x\n", einfo->operation);
-		return false;
+		return -EINVAL;
 	}
 	if (einfo->ip_ect & ~IPT_ECN_IP_MASK) {
 		pr_info("new ECT codepoint %x out of mask\n", einfo->ip_ect);
-		return false;
+		return -EINVAL;
 	}
 	if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR)) &&
 	    (e->ip.proto != IPPROTO_TCP || (e->ip.invflags & XT_INV_PROTO))) {
 		pr_info("cannot use TCP operations on a non-tcp rule\n");
-		return false;
+		return -EINVAL;
 	}
-	return true;
+	return 0;
 }
 
 static struct xt_target ecn_tg_reg __read_mostly = {