Improve Error Handling

[kathrynfejer]

Currently when there is an error in enftun we either:

• call stop_all and reconnect
• log the error, but nothing else is done

If we are reconnecting, when the error could be handled in another way, we lose availability. How this is solved may be different for each case, but it would be good to take a look at how we can improve error handling. The motivation for this issue comes from this comment.