uip6: fix bug that caused the payload of ICMPv6 messages not to match that of the original packet
uip6: fix bug that caused the payload of ICMPv6 messages not to match that of the original packet

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