iwlwifi: control led while update tx/rx bytes counts

LED blinking rate is based on tx/rx traffic, the most reasonable place
to do it is after update the traffic byte counts

This fixes the recent LED blinking breakage on 3945 introduced by "iwlwifi:
separate led function from statistic notification"

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Tested-by: Maxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>