iwlagn: do not send key clear commands when rfkill enabled

Do all key clearing except sending sommands to device when rfkill
enabled. When rfkill enabled the interface is brought down and will
be brought back up correctly after rfkill is enabled again.

Same change is not needed for iwl3945 as it ignores return code when
sending key clearing command to device.

This fixes http://bugzilla.kernel.org/show_bug.cgi?id=13742



Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Tested-by: Frans Pop <elendil@planet.nl>
Signed-off-by: John W. Linville <linville@tuxdriver.com>