sixlowpan_nd: provide convinience functions to get/set ABRO version
sixlowpan_nd: provide convinience functions to get/set ABRO version

A-Paul/RIOT,OTAkeys/RIOT,basilfx/RIOT,BytesGalore/RIOT,toonst/RIOT,ant9000/RIOT,jfischer-phytec-iot/RIOT,kerneltask/RIOT,gebart/RIOT,adjih/RIOT,gebart/RIOT,OlegHahm/RIOT,kerneltask/RIOT,biboc/RIOT,ks156/RIOT,lazytech-org/RIOT,adjih/RIOT,neiljay/RIOT,beurdouche/RIOT,plushvoxel/RIOT,ks156/RIOT,ant9000/RIOT,miri64/RIOT,A-Paul/RIOT,neiljay/RIOT,lazytech-org/RIOT,neumodisch/RIOT,ks156/RIOT,adrianghc/RIOT,neumodisch/RIOT,authmillenon/RIOT,jfischer-phytec-iot/RIOT,adjih/RIOT,OlegHahm/RIOT,rfuentess/RIOT,ks156/RIOT,mfrey/RIOT,basilfx/RIOT,RIOT-OS/RIOT,adjih/RIOT,OTAkeys/RIOT,josephnoir/RIOT,avmelnikoff/RIOT,josephnoir/RIOT,ant9000/RIOT,thomaseichinger/RIOT,lazytech-org/RIOT,A-Paul/RIOT,miri64/RIOT,jasonatran/RIOT,yogo1212/RIOT,avmelnikoff/RIOT,yogo1212/RIOT,x3ro/RIOT,A-Paul/RIOT,authmillenon/RIOT,toonst/RIOT,thomaseichinger/RIOT,Josar/RIOT,LudwigOrtmann/RIOT,rfuentess/RIOT,cladmi/RIOT,LudwigOrtmann/RIOT,Josar/RIOT,avmelnikoff/RIOT,LudwigOrtmann/RIOT,cladmi/RIOT,gebart/RIOT,immesys/RiSyn,RIOT-OS/RIOT,OlegHahm/RIOT,adrianghc/RIOT,Josar/RIOT,LudwigOrtmann/RIOT,basilfx/RIOT,neiljay/RIOT,hamilton-mote/RIOT-OS,josephnoir/RIOT,immesys/RiSyn,gebart/RIOT,BytesGalore/RIOT,A-Paul/RIOT,OlegHahm/RIOT,jfischer-phytec-iot/RIOT,avmelnikoff/RIOT,plushvoxel/RIOT,thomaseichinger/RIOT,miri64/RIOT,aeneby/RIOT,beurdouche/RIOT,neumodisch/RIOT,yogo1212/RIOT,x3ro/RIOT,yogo1212/RIOT,roberthartung/RIOT,josephnoir/RIOT,kYc0o/RIOT,toonst/RIOT,aeneby/RIOT,jasonatran/RIOT,authmillenon/RIOT,kYc0o/RIOT,cladmi/RIOT,mtausig/RIOT,thomaseichinger/RIOT,ant9000/RIOT,jfischer-phytec-iot/RIOT,kaspar030/RIOT,kbumsik/RIOT,adjih/RIOT,adrianghc/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,kerneltask/RIOT,hamilton-mote/RIOT-OS,mtausig/RIOT,aeneby/RIOT,kbumsik/RIOT,OlegHahm/RIOT,mtausig/RIOT,smlng/RIOT,roberthartung/RIOT,kaspar030/RIOT,jasonatran/RIOT,authmillenon/RIOT,plushvoxel/RIOT,adrianghc/RIOT,smlng/RIOT,neumodisch/RIOT,plushvoxel/RIOT,LudwigKnuepfer/RIOT,jasonatran/RIOT,thomaseichinger/RIOT,RIOT-OS/RIOT,basilfx/RIOT,yogo1212/RIOT,kaspar030/RIOT,roberthartung/RIOT,kbumsik/RIOT,jfischer-phytec-iot/RIOT,gebart/RIOT,Josar/RIOT,rfuentess/RIOT,immesys/RiSyn,ks156/RIOT,ant9000/RIOT,kYc0o/RIOT,mfrey/RIOT,smlng/RIOT,LudwigKnuepfer/RIOT,immesys/RiSyn,jasonatran/RIOT,josephnoir/RIOT,beurdouche/RIOT,smlng/RIOT,biboc/RIOT,mfrey/RIOT,RIOT-OS/RIOT,plushvoxel/RIOT,neiljay/RIOT,kerneltask/RIOT,biboc/RIOT,x3ro/RIOT,kYc0o/RIOT,kerneltask/RIOT,adrianghc/RIOT,LudwigKnuepfer/RIOT,hamilton-mote/RIOT-OS,smlng/RIOT,mfrey/RIOT,toonst/RIOT,authmillenon/RIOT,cladmi/RIOT,Josar/RIOT,roberthartung/RIOT,rfuentess/RIOT,kbumsik/RIOT,hamilton-mote/RIOT-OS,kYc0o/RIOT,miri64/RIOT,LudwigKnuepfer/RIOT,lazytech-org/RIOT,OTAkeys/RIOT,avmelnikoff/RIOT,BytesGalore/RIOT,OTAkeys/RIOT,basilfx/RIOT,BytesGalore/RIOT,aeneby/RIOT,OTAkeys/RIOT,roberthartung/RIOT,miri64/RIOT,kbumsik/RIOT,beurdouche/RIOT,kaspar030/RIOT,kaspar030/RIOT,biboc/RIOT,rfuentess/RIOT,neiljay/RIOT,biboc/RIOT,x3ro/RIOT,mtausig/RIOT,neumodisch/RIOT,immesys/RiSyn,neumodisch/RIOT,cladmi/RIOT,beurdouche/RIOT,x3ro/RIOT,lazytech-org/RIOT,toonst/RIOT,LudwigOrtmann/RIOT,hamilton-mote/RIOT-OS,mtausig/RIOT,yogo1212/RIOT,immesys/RiSyn,BytesGalore/RIOT,LudwigKnuepfer/RIOT,LudwigOrtmann/RIOT,mfrey/RIOT,aeneby/RIOT