examples/sniffer: fix deprecated shell_commands
examples/sniffer: fix deprecated shell_commands

RIOT-OS/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,jasonatran/RIOT,kaspar030/RIOT,ant9000/RIOT,kaspar030/RIOT,kaspar030/RIOT,ant9000/RIOT,kaspar030/RIOT,jasonatran/RIOT,ant9000/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,jasonatran/RIOT,ant9000/RIOT,ant9000/RIOT,kaspar030/RIOT,RIOT-OS/RIOT