Allow 1KB in vtc_dump so backend poll info is complete

bin/varnishtest/vtc_log.c

@@ -187,7 +187,7 @@ vtc_dump(struct vtclog *vl, int lvl, const char *pfx, const char *str, int len)
 		if (len < 0)
 			len = strlen(str);
 		for (l = 0; l < len; l++, str++) {
-			if (l > 512 && olen != -2) {
+			if (l > 1024 && olen != -2) {
 				VSB_printf(vl->vsb, "...");
 				break;
 			}