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/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c
index 70288dc..385677b 100644
--- a/net/netfilter/xt_TCPMSS.c
+++ b/net/netfilter/xt_TCPMSS.c
@@ -246,13 +246,13 @@
 			   (1 << NF_INET_POST_ROUTING))) != 0) {
 		pr_info("path-MTU clamping only supported in "
 			"FORWARD, OUTPUT and POSTROUTING hooks\n");
-		return false;
+		return -EINVAL;
 	}
 	xt_ematch_foreach(ematch, e)
 		if (find_syn_match(ematch))
-			return true;
+			return 0;
 	pr_info("Only works on TCP SYN packets\n");
-	return false;
+	return -EINVAL;
 }
 
 #if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE)
@@ -268,13 +268,13 @@
 			   (1 << NF_INET_POST_ROUTING))) != 0) {
 		pr_info("path-MTU clamping only supported in "
 			"FORWARD, OUTPUT and POSTROUTING hooks\n");
-		return false;
+		return -EINVAL;
 	}
 	xt_ematch_foreach(ematch, e)
 		if (find_syn_match(ematch))
-			return true;
+			return 0;
 	pr_info("Only works on TCP SYN packets\n");
-	return false;
+	return -EINVAL;
 }
 #endif