boards/waspmote: Update XTIMER{,_ISR}_BACKOFF
boards/waspmote: Update XTIMER{,_ISR}_BACKOFF

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