allows rtimer_clock_t to be defined from contiki-conf.h
allows rtimer_clock_t to be defined from contiki-conf.h

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