wimax: indicate initial SW rfkill state is "blocked"

The WiMAX stack assumes that all WiMAX devices are SW OFF when they
are initialized. The recent changes in the RFKILL stack thus cause an
initial call after rfkill_register(), because by default, rfkill
considers devices to be SW ON upon registration.

So call rfkill_init_sw_state() to set it to SW OFF so
rfkill_register() doesn't do that unnecessary step.

Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>