iwlwifi: check RF kill register when interrupts have been disabled

Since the interrupts have been disabled, we may have missed an RF
kill interrupt. Check the register to be sure the op_mode is in
sync.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>