rfkill: Update userspace API documentation

Add a note to userspace on the effect of RFKILL_OP_CHANGE_ALL also
updating the default state for hotplugged devices.

Signed-off-by: João Paulo Rechi Vita <[e-mail]>
[reword a bit]
Signed-off-by: Johannes Berg <[e-mail]>

include/uapi/linux/rfkill.h

···
  * @RFKILL_OP_DEL: a device was removed
  * @RFKILL_OP_CHANGE: a device's state changed -- userspace changes one device
  * @RFKILL_OP_CHANGE_ALL: userspace changes all devices (of a type, or all)
+ *	into a state, also updating the default state used for devices that
+ *	are hot-plugged later.
  */
 enum rfkill_operation {
 	RFKILL_OP_ADD = 0,