Ella Core has a Denial of Service via SCTP connection cleanup deadlock

Summary

A deadlock in the AMF's SCTP notification handler causes the entire AMF control plane to hang until the process is restarted.

Impact

An attacker with access to the N2 interface can cause Ella Core to hang, resulting in a denial of service for all subscribers.

Fix

Add deferred Radio cleanup in serveConn SCTP server so that every connection exit path removes the radio. Remove the stale-entry scan from SCTP Notification handling.