Fix port naming for atm switch

Fix #735

gns3server/controller/ports/atm_port.py

@@ -42,6 +42,10 @@ class ATMPort(SerialPort):
         """
         return "a"
 
+    @property
+    def short_name(self):
+        return "{}".format(self._port_number)
+
     @property
     def data_link_types(self):
         """