platform/x86: acer-wmi: add another KEY_WLAN keycode

Now that we have informed the firmware that the RF Button driver is
active, laptops such as the Acer TravelMate P238-M will generate
a WMI key event with code 0x86 when the Fn+F3 airplane mode key is
pressed.

Add this keycode to the table so that it is converted to an appropriate
input event.

Signed-off-by: Chris Chiu <chiu@endlessm.com>
Signed-off-by: Daniel Drake <drake@endlessm.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>