[FS#328] Add in "region fix" for TP-Link routers (esp. Archer C7) to fix 18005 error

[LEDE Bugs]

A new Flyspray task has been opened.  Details are below. 

User who did this - Rich Brown (richb-hanover) 

Attached to Project - LEDE Project
Summary - Add in "region fix" for TP-Link routers (esp. Archer C7) to fix 18005 error
Task Type - Feature Request
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - Medium
Priority - Very Low
Reported Version - Trunk
Due in Version - Undecided
Due Date - Undecided
Details - Supply the following if possible:
 - Device problem occurs on
 - Software versions of LEDE release, packages, etc.
 - Steps to reproduce
   

 TP-Link, in its infinite wisdom, decided to put a kludge into their factory firmware update facility that "prevents" people from loading in third-party firmware. 

Well, shortly after they added this (mis)feature, a workaround was discovered and installed in OpenWrt DD trunk. Unfortunately, the discovery happened after LEDE forked from OpenWrt, so the fix is not in LEDE. (At least, a version tested from late November 2016 was not able to be imported over factory firmware. For more info, see: https://forum.openwrt.org/viewtopic.php?id=63107

My request: back port the fix from OpenWrt DD into LEDE. There's a bunch of info on the TP-Link Archer C7 device page at OpenWrt that may be helpful: https://wiki.openwrt.org/toh/tp-link/archer-c5-c7-wdr7500#quick_start_guide

Thanks.

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=328