wimax: testing for rfkill support should also test for CONFIG_RFKILL_MODULE

Current WiMAX rfkill code is missing the case where rfkill is compiled
in as modules and works only when rfkill is compiled in. This is not
correct. Fixed to test for CONFIG_RFKILL or CONFIG_RKILL_MODULE.

Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>