ieee802154_submac: set TRX state only if SubMAC is idle
ieee802154_submac: set TRX state only if SubMAC is idle

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