Raspberry Ethernet On WiFi Off

From Top 10 common issues while using raspberry-pi

Ethernet On WiFi Off

By default, when an Ethernet cable is connected to the Raspberry Pi, the Wi-Fi connectivity is disabled. This was implemented probably as a security feature for the Pi to disable routing between the Wi-Fi and the Ethernet port. This action is being managed by a config file named ifplugd which has to be disabled if you want to use the Wi-Fi and Ethernet connections at the same time.

To do this, run;

sudo update-rc networking disable
Or 
sudo apt-get purge ifplugd

You should now be able to use both network options at the same time but do not forget the security loophole this could create as the Pi will behave like a router in this mode.

Good to know