'xids is a sequence of (dpid,xid)
first_switch is the DPID where the packet came from
packet is something that can be sent in a packet_out'

def __init__(self, path, packet):

    self.expires_at = (time.time() + PATH_SETUP_TIME)
    self.path = path
    self.first_switch = path[0][0].dpid
    self.xids = set()
    self.packet = packet
    if (len(waiting_paths) > 1000):
        WaitingPath.expire_waiting_paths()
