sniffer: reduce rawdump thread stack size
sniffer: reduce rawdump thread stack size

ant9000/RIOT,kaspar030/RIOT,ant9000/RIOT,jasonatran/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,kaspar030/RIOT,miri64/RIOT,miri64/RIOT,jasonatran/RIOT,miri64/RIOT,ant9000/RIOT,RIOT-OS/RIOT,ant9000/RIOT,jasonatran/RIOT,ant9000/RIOT,jasonatran/RIOT,miri64/RIOT,miri64/RIOT,kaspar030/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT