[kio_mtp] Improve warning message
Review Request #128793 - Created Aug. 29, 2016 and submitted
Sometimes the "Maybe you need to unlock your device?" message appears even if the user has unlocked their device, so it's not very useful. This happened to me as well and I had to look for the fix on google.
Since this warning is displayed also when MTP is disabled on the phone's side, let's warn the user about this.