This may be moot and should be revisited if only px4_getops is used, but this pr politely documents the reson for the logic.

* Change default port to Serial4 and improve status outputs.

* Reduce stack size.

- replay was not working without these values as only range measurements
were given to the filter which were between the min/max value

Signed-off-by: Roman <bapstroman@gmail.com>