gnrc_netif: reduce code duplication
gnrc_netif: reduce code duplication

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