WiFi: Checking the state of Wifi before disabling the Wifi

CRs-Fixed: 183294

Broadcast receiver is registered in while enabling the Wifi and unregistered
in disable. It is possible to disable the Wifi even without enabling it. This
happens when Airplane mode is set. Wifi state is not checked before
unregistering the broadcast receiver. Added the check for the State so that if
it disabled earlier then wouldn't call disable function again and even if the
wifi enable failed.