Bugfix: when a CSMA callback is received, we should remove the packet that was transmitted and not just the first packet that happens to be on the output queue.
Bugfix: when a CSMA callback is received, we should remove the packet
that was transmitted and not just the first packet that happens to be on
the output queue.

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