1. fix the device can not receive IP_EVENT_STA_GOT_IP when the router restarted 2. fix the issue that layer2 node connect to lower-layer node when FIXED-ROOT root disappeared
1. fix the device can not receive IP_EVENT_STA_GOT_IP when the router restarted 2. fix the issue that layer2 node connect to lower-layer node when FIXED-ROOT root disappeared