ospf 不同状态机起的定时器： ism: ospf-ifp ism_down ->(event:l3-ifp-up)-> ism_waiting -> 等待ism选举【起waiting等待定时器】nsm->down ->(event:hello-PacketReceived)-> nsm_init 【接收处理hello报文，OSPF_NSM_EVENT_SCHEDULE (nbr, NSM