Fix data race in sync::state, the stop() did not acquire the required lock.

srsue/hdr/phy/scell/scell_sync.h

@@ -199,7 +199,11 @@ public:
   /**
    * Resets the class, goes back into IDLE mode
    */
-  void stop() { state = STATE_IDLE; }
+  void stop()
+  {
+    std::unique_lock<std::mutex> lock(mutex);
+    state = STATE_IDLE;
+  }
 
   /**
    * Runs internal FSM, performing Synchronization operations on the provided buffer. It expects data per subframe