Added clock_seconds implementation to minimal-net port
Added clock_seconds implementation to minimal-net port

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