ieee802154: add MR-FSK SFD values for 2FSK
ieee802154: add MR-FSK SFD values for 2FSK

Signed-off-by: Jean Pierre Dudey <341388fa1817ca285e65547384a9727ce7f6d39a@hotmail.com>

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