the process when the querier received IGMP.

def packet_in_handler(self, req_igmp, msg):
        """the process when the querier received IGMP."""
        ofproto = msg.datapath.ofproto
        if ofproto.OFP_VERSION == ofproto_v1_0.OFP_VERSION:
            in_port = msg.in_port
        else:
            in_port = msg.match['in_port']
        if (igmp.IGMP_TYPE_REPORT_V1 == req_igmp.msgtype or
                igmp.IGMP_TYPE_REPORT_V2 == req_igmp.msgtype):
            self._do_report(req_igmp, in_port, msg)
        elif igmp.IGMP_TYPE_LEAVE == req_igmp.msgtype:
            self._do_leave(req_igmp, in_port, msg)