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8d2895463b
UE paging can recreate the AS-side SDAP entity while NAS still keeps the PDU session established. Per TS 38.304 clause 7.1 and TS 24.501 clauses 5.6.2.2.1,5.6.1.2 paging/service request restores user-plane resources for an established PDU session, it does not imply deleting the UE IP/TUN interface. Deleting the UE TUN with SDAP entity teardown breaks user-plane continuity after re-attach. We need SDAP entity lifetime and UE TUN lifetime to be decoupled. This commit keeps a UE/PDU-session TUN registry outside the SDAP entity lifetime. When a UE SDAP entity is recreated, reattach it to the preserved TUN socket and restart the reader thread. On first PDU session setup, NAS registers the TUN before attaching the reader. The sequence is the following: (1) NAS register the iface (2) sdap entity attaches to the iface (3) UE goes IDLE, SDAP entity is destroyed, iface is deatched and brought down (4) UE Service Request, SDAP entity is created (5) iface reattaches to the SDAP entity and is brought up UE reattach assumes the PDU session TUN interface was registered before the SDAP entity is recreated. DL/UL data is intentionally dropped when SDAP is not yet attached or QFI is unavailable, rather than queued in this layer. Changes: - `nr_sdap.c`: keep a UE/PDU-session TUN registry, duplicate the stored socket into each SDAP entity, and add attach/detach/destroy helpers. - `nr_sdap_entity.c`: detach SDAP entities from their TUN reader on deletion, preserve UE TUN interfaces across idle cleanup, and destroy gNB TUN interfaces when the gNB entity is removed. Drop downlink SDUs if the UE SDAP entity is not attached to a TUN socket yet. - `openair3/NAS/NR_UE/nr_nas_msg.c`: set QFI before UE TUN creation so first attach can pick up cached QFI. - `common/utils/tuntap_if.c`: add `tuntap_set_up`/`tuntap_set_down` helpers for UE interface state reflection and initialize `flags` in `tuntap_destroy` to avoid maybe-uninitialized build failures. Signed-off-by: Guido Casati <guido.casati@openairinterface.org>