Ella Core panics on invalid PDU Session IDs in NGAP messages

Ella Core is a 5G core designed for private networks. Versions prior to 1.6.0 panic when processing NGAP messages with invalid PDU Session IDs outside of 1-15. An attacker able to send crafted NGAP messages to Ella Core can crash the process, causing service disruption for all connected subscribers. No authentication is required. Version 1.6.0 added PDU Session ID validations during NGAP message handling.