netfilter: ipt_ecn: fix protocol check in ecn_mt_check()

Check for protocol inversion in ecn_mt_check() and remove the
unnecessary runtime check for IPPROTO_TCP in ecn_mt().
Signed-off-by: Patrick McHardy <kaber@trash.net>

net/ipv4/netfilter/ipt_ecn.c

@@ -76,8 +76,6 @@ static bool ecn_mt(const struct sk_buff *skb, struct xt_action_param *par)
 			return false;
 
 	if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR)) {
-		if (ip_hdr(skb)->protocol != IPPROTO_TCP)
-			return false;
 		if (!match_tcp(skb, info, &par->hotdrop))
 			return false;
 	}
@@ -97,7 +95,7 @@ static int ecn_mt_check(const struct xt_mtchk_param *par)
 		return -EINVAL;
 
 	if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR) &&
-	    ip->proto != IPPROTO_TCP) {
+	    (ip->proto != IPPROTO_TCP || ip->invflags & IPT_INV_PROTO)) {
 		pr_info("cannot match TCP bits in rule for non-tcp packets\n");
 		return -EINVAL;
 	}