Disable fast_open when it's not supported

src/local.c

@@ -1452,6 +1452,7 @@ main(int argc, char **argv)
         LOGI("using tcp fast open");
 #else
         LOGE("tcp fast open is not supported by this environment");
+        fast_open == 0;
 #endif
     }
 

src/server.c

@@ -1835,6 +1835,7 @@ main(int argc, char **argv)
         LOGI("using tcp fast open");
 #else
         LOGE("tcp fast open is not supported by this environment");
+        fast_open = 0;
 #endif
     }