Issue: After flashing OpenWrt, WiFi is not working.
Root cause: For devices that have Ethernet ports, the default Wi-Fi configuration is OFF.
Solution: Connect your computer to the LAN port of the device, login the LuCI configuration interface at http://192.168.1.1 and enable the Wi-Fi network in Network > Wireless.
For devices that have no LuCI installed by default you can turn Wi-Fi ON by changing disabled 1 ⇒ disabled 0 in the /etc/config/wireless UCI configuration file, when logged in via SSH.