fix #2204

avoid exception in close_interface when interface.server is not in
self.interfaces

lib/network.py

@@ -508,6 +508,7 @@ class Network(util.DaemonThread):
 
     def close_interface(self, interface):
         if interface:
+            if interface.server in self.interfaces:
                 self.interfaces.pop(interface.server)
             if interface.server == self.default_server:
                 self.interface = None