uorb: _POSIX_NAME_MAX -> NAME_MAX

[jnippula]

In SITL case the _POSIX_NAME_MAX is only 14, so it fails for every topic. Use NAME_MAX instead to get correct maximum filename value for both posix and nuttx cases.

log snippet from sitl-test run:

[   3.129|px4       ] ERROR [uORB] Device node name too long! 'sensor_baro'
[   3.137|px4       ] ERROR [uORB] Device node name too long! 'tune_control'
[   3.143|px4       ] ERROR [uORB] Device node name too long! 'manual_control_setpoint'
[   3.147|px4       ] ERROR [uORB] Device node name too long! 'sensors_status_mag'
[   3.147|px4       ] ERROR [uORB] Device node name too long! 'sensors_status_baro'
[   3.148|px4       ] ERROR [uORB] Device node name too long! 'sensor_selection'
[   3.148|px4       ] ERROR [uORB] Device node name too long! 'sensors_status_imu'
[   3.148|px4       ] ERROR [uORB] Device node name too long! 'vehicle_acceleration'

[jnippula]

That check is only printing error message, so it didn't really affect the functionality. That is why the SITL test were successful, but the error prints were just printed in to the console log.
I noticed this issue when running the SITL locally and saw lot of red error prints in the console.

[jnippula]

Now the error messages are gone from SITL-test:
https://github.com/tiiuae/px4-firmware/pull/489/checks