mds/Beacon: wake up the thread in shutdown()

This eliminates the `wait_for()` delay and speeds up MDS shutdown.

Fixes: https://tracker.ceph.com/issues/68759
Signed-off-by: Max Kellermann <[email protected]>

Author: MaxKellermann

src/mds/Beacon.cc

@@ -61,6 +61,7 @@ void Beacon::shutdown()
   std::unique_lock<std::mutex> lock(mutex);
   if (!finished) {
     finished = true;
+    cvar.notify_all();
     lock.unlock();
     if (sender.joinable())
       sender.join();