riotctrl_shell.netif: fix for multiple interfaces with netstats
riotctrl_shell.netif: fix for multiple interfaces with netstats

RIOT-OS/RIOT,jasonatran/RIOT,authmillenon/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,authmillenon/RIOT,jasonatran/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,ant9000/RIOT,OlegHahm/RIOT,authmillenon/RIOT,miri64/RIOT,ant9000/RIOT,authmillenon/RIOT,OTAkeys/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,miri64/RIOT,OlegHahm/RIOT,ant9000/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,miri64/RIOT,kYc0o/RIOT,ant9000/RIOT,kaspar030/RIOT,jasonatran/RIOT,kYc0o/RIOT,OlegHahm/RIOT,miri64/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,kYc0o/RIOT,ant9000/RIOT,OlegHahm/RIOT,kaspar030/RIOT,authmillenon/RIOT,kYc0o/RIOT,kaspar030/RIOT,miri64/RIOT,OTAkeys/RIOT,kaspar030/RIOT,OlegHahm/RIOT