Build OpenWrt for netgear R6800

@yukunyi See here for an update on the LEDs:

@xkuza I recently flashed a recent master build without issues from stock, so you might want to try your hand at an early 21.02 image. You might need to rename it so it looks like a Netgear image filename (e.g. netgear-v2.0.1.img or something like that).