Fix memory leak when deleting client instance.

Delete the disconnect timer when the client destructor is called.

Author: h2zero

src/NimBLEClient.cpp

@@ -93,6 +93,8 @@ NimBLEClient::~NimBLEClient() {
         delete m_pClientCallbacks;
     }
 
+    ble_npl_callout_deinit(&m_dcTimer);
+
 } // ~NimBLEClient