shell/commands/sc_gnrc_rpl.c: fix cpp.check unitialized variable
shell/commands/sc_gnrc_rpl.c: fix cpp.check unitialized variable

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