Introduce paging_transfer in the mac_rrc_dl interface so the CU can pass
paging to the DU (F1 or direct). Use the F1AP paging lib on both CU and DU
for decode/free and to avoid leaking the message after send.
- Add f1_paging_transfer_func_t and paging_transfer to nr_mac_rrc_dl_if_s
(mac_rrc_dl.h, nr_rrc_defs.h).
- F1AP path: paging_f1ap() allocates F1AP_PAGING, copies with cp_f1ap_paging(),
sends via ITTI to TASK_CU_F1. Direct path: f1_paging_transfer_direct() stub
- CU task: call free_f1ap_paging() after CU_send_Paging() to release the message.
- DU: DU_handle_Paging() uses decode_f1ap_paging()/free_f1ap_paging() from lib,
returns on decode failure; remove inline ASN.1 IE parsing.
- cleanup outdated header comments in header files
- Left a TODO not in DU code to build PCCH (in F1 and direct paths)