bugfix: slip must be initialized after ctimer, as it uses ctimers
bugfix: slip must be initialized after ctimer, as it uses ctimers

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