rfkill: add WARN and BUG_ON paranoia (v2)

BUG_ON() and WARN() the heck out of buggy drivers calling into the rfkill
subsystem.

Also switch from WARN_ON(1) to the new descriptive WARN().

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