'Adds a port
Sends a port_status message to the controller'

def add_port(self, port):

    try:
        port_no = port.port_no
    except:
        port_no = port
        port = self.generate_port(port_no, self.dpid)
    if (port_no in self.ports):
        raise RuntimeError(('Port    %s    already    exists' % (port_no,)))
    self.ports[port_no] = port
    self.port_stats[port.port_no] = ofp_port_stats(port_no=port.port_no)
    self.send_port_status(port, OFPPR_ADD)
