iwlcore: dont commit power command if interface is not up

If user set new power level, accept the new power level and only
send command to host if the interface is up and radio on.

Signed-off-by: Mohamed Abbas <mohamed.abbas@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>