NR Paging on CU

Implements the NR paging path on the CU:

• NGAP Paging is decoded and passed to RRC
• RRC builds F1AP Paging, and distributes it to DUs via F1 callback

Changes:

• Refactor and extend F1AP Paging encode/decode libraries
  • add missing enc/dec/eq/cp functions
  • add unit test
  • IEs: CN UE 5G-S-TMSI, RAN UE I-RNTI; optional DRX/priority/origin)
• Refactor Cu callback CU_send_Paging
• Refactor DU handler DU_handle_Paging
• Refactor old F1 callback for Paging indication, extend it and align with existing F1 callbacks in stack
• Refactor and extend NGAP Paging encode/decode lib
  • add missing enc/dec/eq/cp functions
  • add unit test
  • Fixes NGAP paging to accept Paging only on SCTP stream 0 per TS 38.412
• Includes supporting refactors (PDU session split, shared 5G-S-TMSI helpers, NGAP/F1AP cleanups)

Testing

• NGAP and F1AP Paging lib unit tests (enc/dec)
• Stream-0 fix validated with Open5GS AMF

This MR does not address the DU changes besides the F1 handler. F1AP Paging does not have an RRC container to pass the PCCH message to the DU, and F1 DL RRC Message Transfer does not apply to PCCH. PCCH-Message shall be built at DU per TS 38.331 §5.3.2, with padding as per §8.5 and delivered as RLC SDU per §8.2. For each cell in Paging Cell List that belongs to this DU, queue for MAC. MAC schedules at PF/PO per TS 38.304 §7.

Refs:

• F1AP 3GPP TS 38.473 version 16.21.0 Release 16
• NGAP 3GPP TS 38.413 version 16.17.0 Release 16