Send Velocity in the world frame of reference setpoint.

        vx, vy, vz are in m/s
        yawrate is in degrees/s

def send_velocity_world_setpoint(self, vx, vy, vz, yawrate):
        """
        Send Velocity in the world frame of reference setpoint.

        vx, vy, vz are in m/s
        yawrate is in degrees/s
        """
        pk = CRTPPacket()
        pk.port = CRTPPort.COMMANDER_GENERIC
        pk.data = struct.pack('<Bffff', TYPE_VELOCITY_WORLD,
                              vx, vy, vz, yawrate)
        self._cf.send_packet(pk)