Increase logging of errors

[ftapajos]

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fix #2579

Commit 6113eac95a9df634fbc858be542c4a0456bfe7b9 started using MQTTRC enums as a handle__publish return value, which typically were MOSQERR values. I personally think this is a good use, however the logging system should comply with it.

[ralight]

Looks good to me, thank you very much.