minor etimer code cleanup
minor etimer code cleanup

MohamedSeliem/contiki,bluerover/6lbr,MohamedSeliem/contiki,MohamedSeliem/contiki,bluerover/6lbr,arurke/contiki,MohamedSeliem/contiki,bluerover/6lbr,MohamedSeliem/contiki,arurke/contiki,MohamedSeliem/contiki,bluerover/6lbr,arurke/contiki,arurke/contiki,bluerover/6lbr,arurke/contiki,bluerover/6lbr,arurke/contiki,MohamedSeliem/contiki,arurke/contiki,bluerover/6lbr