Errors in session tracking after moving session tracking into session_started + session_ended

[jonasbardino]

Since the adjustments in bb72b48 to handle all session tracking in the paramiko session_started and session_ended we see stray tracking errors in sftp-subsys.log like:

2024-12-12 09:47:55,318 ERROR failed to track close session

Apparently they appear when concurrent sessions are launched by the same client and the session tracking structure doesn't have sufficient information to match which session were closed in what order.

They are not exactly dangerous but noisy and possibly interfere with proper session limitation and clean up.