NGAP Release Cplt: indicate release PDU sessions

We can optionally indicate the PDU session IDs. At least with OAI 5GC,
that should help it clean up.

openair2/COMMON/ngap_messages_types.h

@@ -583,6 +583,8 @@ typedef struct ngap_ue_ctxt_modification_resp_s {
 
 typedef struct ngap_ue_release_complete_s {
   uint32_t gNB_ue_ngap_id;
+  int num_pdu_sessions;
+  uint32_t pdu_session_id[256];
 } ngap_ue_release_complete_t;
 
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