ConnectionManager: check if connexion is running before use

Change-Id: I4f344be3c820b744f442286f8e226f9185fa9cfd
diff --git a/include/multiplexed_socket.h b/include/multiplexed_socket.h
index 480932c..e57d1d4 100644
--- a/include/multiplexed_socket.h
+++ b/include/multiplexed_socket.h
@@ -123,6 +123,7 @@
      * This will close all channels and send a TLS EOF on the main socket.
      */
     void shutdown();
+    bool isRunning() const;
 
     /**
      * This will wait that eventLoop is stopped and stop it if necessary