Bugfix: make sure that neighbor exists before attempting to update tx count.
Bugfix: make sure that neighbor exists before attempting to update tx
count.

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