Swap Accel and Gyro where angular_velocity and linear_acceleration are set

`msg_imu.angular_velocity.*` should be equal to `msg_in.Gyro.*`, NOT `msg_in.Accel.*`. Likewise for msg_imu.linear_acceleration.*. These are swapped by mistake.

Discovered this bug by noticing that angular velocity and acceleration were swapped in the `/Imu` ROS topic.