rfkill: document rfkill_force_state as required (v2)

While the rfkill class does work with just get_state(), it doesn't work
well on devices that are subject to external events that cause rfkill state
changes.

Document that rfkill_force_state() is required in those cases.

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

net/rfkill/rfkill.c

@@ -252,7 +252,12 @@ EXPORT_SYMBOL_GPL(rfkill_epo);
  * a notification by the firmware/hardware of the current *real*
  * state of the radio rfkill switch.
  *
- * It may not be called from an atomic context.
+ * Devices which are subject to external changes on their rfkill
+ * state (such as those caused by a hardware rfkill line) MUST
+ * have their driver arrange to call rfkill_force_state() as soon
+ * as possible after such a change.
+ *
+ * This function may not be called from an atomic context.
  */
 int rfkill_force_state(struct rfkill *rfkill, enum rfkill_state state)
 {