Paging messages are classified as non-UE-associated signalling per
3GPP TS 38.412 clause 7 (TL), which requires them to be sent on
stream 0 (or a reserved stream pair).
Paging message is received when UE is in RRC_IDLE or RRC_INACTIVE
state, as the RAN has no active UE context and paging targets the
UE by 5G-S-TMSI rather than RAN-UE-NGAP-ID.
The previous implementation incorrectly rejected paging messages
received on stream 0, causing paging failures when using Open5GS AMF.
Changes:
- Accept paging on stream 0 (non-UE-associated signalling)
- Reject paging on non-zero streams (UE-associated streams)
- Add documentation