Added semaphore support for tx queue operations

[cuav-chen2]

Use semaphore to ensure thread safety for operations on tx_queue

[bugobliterator]

The recommendation here is to use canard C++ API for thread-safe application. You will need to have a WITH_SEMAPHORE define like we have in Ardupilot, and a typedef for Semaphore.

Can I ask which RTOS are you using, I will add an example for ChibiOS RTOS.

[cuav-chen2]

The recommendation here is to use canard C++ API for thread-safe application. You will need to have a WITH_SEMAPHORE define like we have in Ardupilot, and a typedef for Semaphore.

Can I ask which RTOS are you using, I will add an example for ChibiOS RTOS.

OK. Thank you so much.