Wi-Fi Router X6 N900

Changed:

1. Add timeout to check DNS alive
2. Add procedure to verify ipv4 and ipv6 on ppp session

Fixed:

1. fix USB2 get function on app agent
2. Ignore DHCP-PD check when use IPv6 Static/6RD type of connection
3. Fix IPv4 PPTP/L2TP hostname set/get error on app agent
4. show the guest network client on DHCP table on web and app agent
5. Fixed Apple iOS 9 login issue with the MyWiFi app.
6. Fixes stability issue where the internet connection is lost and the router has to be rebooted in order to bring it back.