check the rf_config_file name, and ignore if it is null

targets/RT/USER/rrh_gw.c

@@ -299,12 +299,18 @@ static void get_options(int argc, char *argv[]) {
       loopback_flag=1; 
       break;
     case 'f':
-      if (strlen(optarg)<=1024)
+      if (optarg){
+	if ((strcmp("null", optarg) == 0) || (strcmp("NULL", optarg) == 0)) {
+	  printf("no configuration filename is provided\n");
+	}
+	else if (strlen(optarg)<=1024){
+	  // rf_config_file = strdup(optarg);
 	  strcpy(rf_config_file,optarg);
-      else {
+	}else {
 	  printf("Configuration filename is too long\n");
 	  exit(-1);   
 	}
+      }
       break;
     case 't':
       /* When measurements are enabled statistics related to TX/RX time are printed */