Bug 1089486 - [NFC] Disable NFC toggle in settings during NFC HW change,  r=arthur.chen, r=gweng

https://bugzilla.mozilla.org/show_bug.cgi?id=1089486
```DISABLE_DISCOVERY``` is a state in which NFC HW is on but is not actively pooling for NFC tags or peer devices. This is a low power consuming mode in which NFC HW should be when the screen is off or locked. Still in this low power mode it's possible to do NFC payments. This is why it's one of the active states, so NFC icon should be visible in the status bar (while lockscreen is visible). If you want I can add state descriptions in comments.