gnrc_ipv6: use gnrc_netif_hdr_get_netif()
gnrc_ipv6: use gnrc_netif_hdr_get_netif()

cladmi/RIOT,authmillenon/RIOT,x3ro/RIOT,aeneby/RIOT,OlegHahm/RIOT,jasonatran/RIOT,OlegHahm/RIOT,basilfx/RIOT,miri64/RIOT,miri64/RIOT,yogo1212/RIOT,josephnoir/RIOT,x3ro/RIOT,mtausig/RIOT,yogo1212/RIOT,basilfx/RIOT,kYc0o/RIOT,jasonatran/RIOT,toonst/RIOT,smlng/RIOT,yogo1212/RIOT,RIOT-OS/RIOT,smlng/RIOT,mtausig/RIOT,josephnoir/RIOT,authmillenon/RIOT,authmillenon/RIOT,toonst/RIOT,aeneby/RIOT,cladmi/RIOT,ant9000/RIOT,x3ro/RIOT,aeneby/RIOT,kaspar030/RIOT,ant9000/RIOT,mtausig/RIOT,josephnoir/RIOT,smlng/RIOT,OTAkeys/RIOT,yogo1212/RIOT,kaspar030/RIOT,miri64/RIOT,OTAkeys/RIOT,rfuentess/RIOT,x3ro/RIOT,toonst/RIOT,josephnoir/RIOT,ant9000/RIOT,RIOT-OS/RIOT,ant9000/RIOT,RIOT-OS/RIOT,miri64/RIOT,authmillenon/RIOT,toonst/RIOT,OTAkeys/RIOT,toonst/RIOT,jasonatran/RIOT,jasonatran/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,x3ro/RIOT,kYc0o/RIOT,basilfx/RIOT,yogo1212/RIOT,kYc0o/RIOT,yogo1212/RIOT,kaspar030/RIOT,basilfx/RIOT,rfuentess/RIOT,rfuentess/RIOT,rfuentess/RIOT,miri64/RIOT,kaspar030/RIOT,aeneby/RIOT,cladmi/RIOT,rfuentess/RIOT,kaspar030/RIOT,OlegHahm/RIOT,jasonatran/RIOT,authmillenon/RIOT,aeneby/RIOT,josephnoir/RIOT,basilfx/RIOT,ant9000/RIOT,OTAkeys/RIOT,cladmi/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,kYc0o/RIOT,mtausig/RIOT,authmillenon/RIOT,smlng/RIOT,smlng/RIOT,mtausig/RIOT,RIOT-OS/RIOT,cladmi/RIOT