When deleting net-l3vpn port, TypeError: delete_port() takes exactly 3 arguments (4 given).
delete_port() is called in File "/usr/lib/python2.7/site-packages/gluon/shim/api_models/net_l3vpn.py",
line 229, in handle_port_delete self.backend.delete_port(key, self.model, deleted_obj).
Change-Id: I1cb080104cfa1decdc3b8f45d102636d3d1e6af7