Openwrt pppoe MTU issue

OpenWrt will get pppoe mtu from wan interface mtu option in the uci,
but if you set mtu in the wan interface, the physical interface's mtu will change, too.

And the pppoe header's length is 8 bytes, if you set mtu to 1500, will get 1500-8=1492 pppoe mtu.

 This is wrong, so you need to change the mtu parameter that ppp daemon parsing in the uci.
You may add a new option in uci something like pppoe_mtu, and modified the ppp script that parsing uci.

How windows WPS function work?

According to this:
https://social.msdn.microsoft.com/Forums/windowsdesktop/en-US/c3d25ade-10c9-4404-92c4-a16ba202ae7b/wifi-proteceted-setupwps-implementation-in-native-wifi-driver-usb?forum=wdk
 discusstion

Windows 7 will display WPS notification if
1. AP broadcast the beacon with WPS capability
2. if AP have WPS capability in the beacon, Windows 7 will start a WPS action, try to get M1 message from AP
3. Windows 7 will look at the M1 message, if config methods have Push Button support Windows 7 will show the WPS notification.

Troubleshooting:
if you have WPS informtaion in the beacon & push button support in the M1 message, but Windows 7 doesn't show up the WPS notification, there most be something wrong with the wireless driver, the wireless driver may not get the packet format correctly.