mavlink_mission: improve comments about casting
mavlink_mission: improve comments about casting

mcgill-robotics/Firmware,jlecoeur/Firmware,jlecoeur/Firmware,mcgill-robotics/Firmware,jlecoeur/Firmware,dagar/Firmware,dagar/Firmware,dagar/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,jlecoeur/Firmware,jlecoeur/Firmware,krbeverx/Firmware,Aerotenna/Firmware,jlecoeur/Firmware,krbeverx/Firmware,mcgill-robotics/Firmware,PX4/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,mcgill-robotics/Firmware,acfloria/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,mje-nz/PX4-Firmware,mcgill-robotics/Firmware,mcgill-robotics/Firmware,Aerotenna/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,mje-nz/PX4-Firmware,dagar/Firmware,dagar/Firmware,acfloria/Firmware,PX4/Firmware,Aerotenna/Firmware,Aerotenna/Firmware,Aerotenna/Firmware,PX4/Firmware,mcgill-robotics/Firmware,Aerotenna/Firmware,krbeverx/Firmware,jlecoeur/Firmware,krbeverx/Firmware,dagar/Firmware,acfloria/Firmware,acfloria/Firmware,dagar/Firmware,jlecoeur/Firmware,krbeverx/Firmware,krbeverx/Firmware,PX4/Firmware,Aerotenna/Firmware