std::shared_ptr Memory Leak (#3680)

* std::shared_ptr Memory Leak

clientSocketHande and _rxBuffer are std::shared_ptr, the stop() call was not correctly releasing them and the operator= had similar problems fix for #3679

* operator= second attempt

* operator= third time

libraries/WiFi/src/WiFiClient.cpp

@@ -196,8 +196,8 @@ WiFiClient & WiFiClient::operator=(const WiFiClient &other)
 
 void WiFiClient::stop()
 {
-    clientSocketHandle = NULL;
-    _rxBuffer = NULL;
+    clientSocketHandle.reset(); // clientSocketHandle = NULL;
+    _rxBuffer.reset(); // _rxBuffer = NULL;
     _connected = false;
 }