rfkill: clarify meaning of rfkill states

rfkill really should have been named rfswitch.  As it is, one can get
confused whether RFKILL_STATE_ON means the KILL switch is on (and
therefore, the radio is being *blocked* from operating), or whether it
means the RADIO rf output is on.

Clearly state that RFKILL_STATE_ON means the radio is *unblocked* from
operating (i.e. there is no rf killing going on).

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Cc: Dmitry Torokhov <dtor@mail.ru>
Signed-off-by: John W. Linville <linville@tuxdriver.com>