dhcp renew issue and add iptalbes rule

    昨天，碰到一个dhcp client renew ip 的时候，网关无法配置成功的问题。目前仍旧没有思路。在此做一个笔记，顺便理一理思路。

    1, renew 的时候，request的是同一个ip，通常网关是不变的，此时。若发现网关未变化，不需要删除default route , then add default again. so, need judge weather the default is changed. we can set a flag.

    2. another case: when dhcp client perform renew, dhcp client get a new ip, but the default route does not change, but this time, kernel will delete default route, we should add default again when we process dhcp option.

    3. but judge ip is change or default route is change , are in two file. how to define a flag can be modified in this 2 files ? share memory ?

    4. if is in share memory, what time to reset the flag, we should make sure, everytime perform renew. we can consider everytime we receive an dhcp-ack.

today we do intergrate test with cwp, we found iptables didn't work. we should consider.

and new event is define, we should modify code to fix it.