Investigate the warning behavior of the update check

[mcktr]

The update check often returns a warning state but no update is available.

The check returns the following output:

WARNING - Update State: Stopped

I guess the update mechanism on the FritzBox itself only run in a certain interval and between a restart and the first run of the update mechanism the state is stopped. But this needs further investigation.

But imho the warning state is wrong here, unknown would be better.

[mcktr]

After triggering a update search on the FritzBox, the state switch to "NoUpdate" which returns OK,

[mcktr]

Reading through the AVM doc here: https://avm.de/fileadmin/user_upload/Global/Service/Schnittstellen/userifSCPD.pdf

I found out that the check update function maybe checks the wrong attribute. What it should check is if there is an update or not, but now the function checks if the update mechanism is running (?).

The correct attribute would be NewUpgradeAvailable

[mcktr]

Fixed in #52