cc26xx: change CCA logic to be standard-compatible; change receiving_packet to return true iff sync (SFD) has been seen
cc26xx: change CCA logic to be standard-compatible; change receiving_packet to return true iff sync (SFD) has been seen

MohamedSeliem/contiki,arurke/contiki,arurke/contiki,MohamedSeliem/contiki,arurke/contiki,arurke/contiki,MohamedSeliem/contiki,MohamedSeliem/contiki,MohamedSeliem/contiki,arurke/contiki,MohamedSeliem/contiki,arurke/contiki,MohamedSeliem/contiki,arurke/contiki