netfilter: xtables: change matches to return error code

The following semantic patch does part of the transformation:
// <smpl>
@ rule1 @
struct xt_match 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_string.c b/net/netfilter/xt_string.c
index 7d14121..e1f22a7 100644
--- a/net/netfilter/xt_string.c
+++ b/net/netfilter/xt_string.c
@@ -48,26 +48,25 @@
 
 	/* Damn, can't handle this case properly with iptables... */
 	if (conf->from_offset > conf->to_offset)
-		return false;
+		return -EINVAL;
 	if (conf->algo[XT_STRING_MAX_ALGO_NAME_SIZE - 1] != '\0')
-		return false;
+		return -EINVAL;
 	if (conf->patlen > XT_STRING_MAX_PATTERN_SIZE)
-		return false;
+		return -EINVAL;
 	if (par->match->revision == 1) {
 		if (conf->u.v1.flags &
 		    ~(XT_STRING_FLAG_IGNORECASE | XT_STRING_FLAG_INVERT))
-			return false;
+			return -EINVAL;
 		if (conf->u.v1.flags & XT_STRING_FLAG_IGNORECASE)
 			flags |= TS_IGNORECASE;
 	}
 	ts_conf = textsearch_prepare(conf->algo, conf->pattern, conf->patlen,
 				     GFP_KERNEL, flags);
 	if (IS_ERR(ts_conf))
-		return false;
+		return -EINVAL;
 
 	conf->config = ts_conf;
-
-	return true;
+	return 0;
 }
 
 static void string_mt_destroy(const struct xt_mtdtor_param *par)