[danfossairunit] Fix network reliability issues and setting of all channel values...

[danfossairunit] Fix network reliability issues and setting of all channel values to zero (#11172)

* Fix Potential null pointer accesses
* Added constants for TCP port and poll interval in seconds.
* Extract interface from DanfossAirUnitCommunicationController.
* Remove unused constants which seems to be left-overs from skeleton.
* Added constant for discovery timeout value for readability.
* Created handler subfolder for DanfossAirUnitHandler (like discovery) for consistency with other bindings.
* Handle lost connection gracefully without updating all channels to zero.
* Fix infinitly blocking network calls preventing proper error handling.
* Fix thing status being reset to ONLINE after failing to update all channels.
* Fix error handling when receiving invalid manual fan step.

Fixes #11167
Fixes #11188

Signed-off-by: Jacob Laursen <jacob-github@vindvejr.dk>