There is no additional setting required.
The wifi LED has been turned off by the OpenWrt firmware our firmware is based upon. This was done by the programmers of OpenWrt do avoid performance issues caused by the LED controller (hi CPU usage). This does not mean the wifi is not functional though.
We have identified a potential issue in the firmware that can cause issues with network and httpd webserver start up on this router. This issue may have affected your router. We have fixed this in the latest firmware release 10.02.1.
Please download the latest firmware for the DIR615c from our
forum page and reflash your router.
Thank You