Disambiguate utp failures: connection vs download, while tracing a query

[carver]

A reasonable approach to this is to return a custom error type from the UtpController::connect_inbound_stream(). The error type can embed whether it failed during connection or download. Perhaps there are even more cases we want to track?

Then, with that error info, we can send the correct failure type to query_trace_events_tx in the overlay service.

This is a continuation of the work in #1479