Merge remote-tracking branch 'origin/e1ap-issue-878' into integration_2025_w04 (!3171)

- Refactor SCTP Association Response Handling
  - Unified function for both CU-CP and CU-UP handling
  - CU-CP: Notifies RRC of E1 connection loss with CU-UP
  - CU-UP: Initiates a new SCTP association request to regain E1 connection
  - this fix will prevent issue #878 from happening

- Send list of PDU Session Resources to Failed Setup in the (PDU Session
  Resource/Initial Context) Setup Response
  - depending on different failure scenarios
  - e.g. (#878) when No CU-UP is associated and still the CU-CP receives a PDU
    Session Setup Request
  - add relevant functions to handle NGAP Setup Response messages with failed
    list of items
  - this is an extra failure handling to make #878 is handled if it ever happens
    again

- NGAP Cause Refactoring
  - Refactor struct for NGAP cause group and value
  - Add extended radio network cause enumeration values
  - Refactor redundant code into a new NGAP cause encoding function

- Minor logging, function descriptions improvements

Closes #878

executables/nr-cuup.c

@@ -172,6 +172,7 @@ int main(int argc, char **argv)
   MessageDef *msg = RCconfig_NR_CU_E1(&e1type);
   AssertFatal(msg != NULL, "Send init to task for E1AP UP failed\n");
   itti_send_msg_to_task(TASK_CUUP_E1, 0, msg);
+  LOG_D(E1AP, "Send E1AP REGISTER REQ to TASK_CUUP_E1\n");
 
   #ifdef E2_AGENT
   //////////////////////////////////