Because it uses a semaphore.

Updated and added full stops to comments and did some comment/whitespace formatting in the startup scripts.

Reduces 'uorb_tests latency_test' by about 1us

The check is unnecessary. In the worst case the semaphore gets unlocked
twice, but it's not an issue because the waiter is only interested in the
first sem_post(), and the semaphore is then not used anymore.

poll() is one of the heavily used methods and thus needs to be optimized
as much as possible.

Test on Pixracer: uorb_tests latency_test
Before:
uORB note: ---------------- LATENCY TEST ------------------
INFO  [uorb_tests] mean:     40.4320 us
INFO  [uorb_tests] std dev:   1.3466 us
INFO  [uorb_tests] min:      39 us
INFO  [uorb_tests] max:      57 us
INFO  [uorb_tests] missed topic updates: 0
This Patch:
uORB note: ---------------- LATENCY TEST ------------------
INFO  [uorb_tests] mean:     31.3480 us
INFO  [uorb_tests] std dev:   1.4584 us
INFO  [uorb_tests] min:      30 us
INFO  [uorb_tests] max:      45 us
INFO  [uorb_tests] missed topic updates: 0

- min/max
- std dev
- number of missed updates

- running at max priority significantly decreases jitter for the latency
  test, providing more consistent results
- stack size increase is required for the latency test

update msgs fields from camelCase to snake_case so rosidl_generate_interfaces() is able to generate code for ROS IDL files

Added remaining two channels of PWM_AUX_DIS disarm parameter set commands, remove trailing whitespace from pwm_params_aux.c and pwm_params_main.c, gps/params.c and added block comment headers to separate sections instead of whitespace.

 - fixes #10033

 - fixes #10028

Also cleanup other RC unit tests

- Telemetry is only enabled on omnibus, since on Pixhawk it seems we cannot
  write to the RC UART due to how the board is wired
- For the Telemetry the UART needs to be opened RW

0 is a valid file descriptor, init (all) to -1 instead