gnrc_ipv6: allow for empty IPv6 header
gnrc_ipv6: allow for empty IPv6 header

mfrey/RIOT,OlegHahm/RIOT,kYc0o/RIOT,biboc/RIOT,RIOT-OS/RIOT,biboc/RIOT,toonst/RIOT,gebart/RIOT,basilfx/RIOT,aeneby/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,smlng/RIOT,miri64/RIOT,A-Paul/RIOT,A-Paul/RIOT,BytesGalore/RIOT,cladmi/RIOT,ant9000/RIOT,kaspar030/RIOT,rfuentess/RIOT,mtausig/RIOT,mtausig/RIOT,jasonatran/RIOT,gebart/RIOT,lazytech-org/RIOT,ant9000/RIOT,authmillenon/RIOT,smlng/RIOT,rfuentess/RIOT,miri64/RIOT,A-Paul/RIOT,rfuentess/RIOT,biboc/RIOT,kYc0o/RIOT,kaspar030/RIOT,basilfx/RIOT,yogo1212/RIOT,toonst/RIOT,aeneby/RIOT,x3ro/RIOT,RIOT-OS/RIOT,yogo1212/RIOT,authmillenon/RIOT,BytesGalore/RIOT,mfrey/RIOT,x3ro/RIOT,OlegHahm/RIOT,kYc0o/RIOT,authmillenon/RIOT,aeneby/RIOT,jasonatran/RIOT,lazytech-org/RIOT,cladmi/RIOT,mtausig/RIOT,cladmi/RIOT,josephnoir/RIOT,jasonatran/RIOT,toonst/RIOT,josephnoir/RIOT,miri64/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,biboc/RIOT,kaspar030/RIOT,authmillenon/RIOT,mfrey/RIOT,mfrey/RIOT,x3ro/RIOT,cladmi/RIOT,gebart/RIOT,yogo1212/RIOT,lazytech-org/RIOT,josephnoir/RIOT,aeneby/RIOT,toonst/RIOT,ant9000/RIOT,josephnoir/RIOT,x3ro/RIOT,OlegHahm/RIOT,basilfx/RIOT,authmillenon/RIOT,mfrey/RIOT,kYc0o/RIOT,yogo1212/RIOT,ant9000/RIOT,A-Paul/RIOT,kYc0o/RIOT,miri64/RIOT,jasonatran/RIOT,smlng/RIOT,A-Paul/RIOT,BytesGalore/RIOT,smlng/RIOT,gebart/RIOT,x3ro/RIOT,rfuentess/RIOT,cladmi/RIOT,OTAkeys/RIOT,basilfx/RIOT,OlegHahm/RIOT,basilfx/RIOT,jasonatran/RIOT,BytesGalore/RIOT,toonst/RIOT,ant9000/RIOT,OlegHahm/RIOT,lazytech-org/RIOT,biboc/RIOT,OTAkeys/RIOT,kaspar030/RIOT,lazytech-org/RIOT,gebart/RIOT,rfuentess/RIOT,yogo1212/RIOT,miri64/RIOT,aeneby/RIOT,BytesGalore/RIOT,RIOT-OS/RIOT,mtausig/RIOT,smlng/RIOT,kaspar030/RIOT,OTAkeys/RIOT,mtausig/RIOT,josephnoir/RIOT,yogo1212/RIOT