gnrc_sixlowpan_frag_rb: add doc on rb_remove() NOP
gnrc_sixlowpan_frag_rb: add doc on rb_remove() NOP

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