loggerd: fix delayed exit from main thread

selfdrive/loggerd/loggerd.cc

@@ -223,6 +223,8 @@ void loggerd_thread() {
   while (!do_exit) {
     // poll for new messages on all sockets
     for (auto sock : poller->poll(1000)) {
+      if (do_exit) break;
+
       // drain socket
       int count = 0;
       QlogState &qs = qlog_states[sock];