iwlwifi: move RF/CT kill check to command wrapper

Currently, we cannot send any commands when the
uCode is in RF or CT kill, but that will not be
true for all new uCode versions, so we need to
move the check into the uCode specific code.

Also remove the duplicate rfkill check.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>