Add support for the TP-Link TL-WDR4300 and TL-WDR3600.

These are actually almost the same units; except one is 3x3 5GHz, and
one is 2x2 5GHz.

Tested:

• TP-Link TL-WDR3600

TODO:

• The ath0/ath1 MAC addresses are ye garbage (00:02:03:04:05:06); fixing that will take a little more time. It works fine with the ath0/ath1 MAC addresses set manually.

• Go through and yank the AR9344 on-board switch config (arswitch1); it's not required here for this AP.