Teach rfkill about wimax radios.

Had to define a KEY_WIMAX as a 'key for disabling only wimax radios',
as other radio technologies have. This makes sense as hardware has
specific keys for disabling specific radios.

The RFKILL enabling part is, otherwise, a copy and paste of any other
radio technology.
Signed-off-by: NInaky Perez-Gonzalez <inaky@linux.intel.com>
Signed-off-by: NIvo van Doorn <IvDoorn@gmail.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>