use stoppable workers to stop answerer

rpc/wrtc_signaling_answerer.go

@@ -281,14 +281,7 @@ func (ans *webrtcSignalingAnswerer) Stop() {
 	ans.startStopMu.Lock()
 	defer ans.startStopMu.Unlock()
 
-	// Code adding workers must atomically check the `closeCtx` before adding to the `bgWorkers`
-	// wait group. Canceling the context must not split those two operations. We ensure this
-	// atomicity by acquiring the `bgWorkersMu` write lock.
-	ans.bgWorkersMu.Lock()
-	ans.cancelBgWorkers()
-	// Background workers require the `bgWorkersMu`. Release the mutex before calling `Wait`.
-	ans.bgWorkersMu.Unlock()
-	ans.bgWorkers.Wait()
+	ans.sw.Stop()
 
 	ans.connMu.Lock()
 	defer ans.connMu.Unlock()