added TP-Link TL-WR841ND/N Devices for 8M and 16M Variants

Edit by Chrissi^:
Patch taken from:
https://github.com/freifunkh/site/blob/master/patches/0003-added-TP-Link-TL-WR841ND-N-Devices-for-8M-and-16M-Va.patch
This Patch adds support for 8M and 16M Flash variants of TP-Link
TL-WR841 with hand-made modifications.