write stats log from main event loop

[davidk81]

@woobianca saw yo might be working on CLI logging, here's an idea to clean up the stats logging during connection errors.

• make --stats logging a bit cleaner for the user by logging in the main recv loop instead of in a separate thread.
• this also suppresses stats logging during connection errors.
• the downside is, no stats will be logged if no telemetry or antenna messages are sent, so even if data transfer is stalled, --stats does not show the updated metrics.

[davidk81]

closing i think this has negligible impact