This commit refactors the TUN interface management by moving its creation
and configuration from the PDCP layer to the SDAP layer for UE.
Key changes include:
- Introduced `tun_generate_ue_ifname` and `tun_destroy` functions for better
TUN interface lifecycle management.
- Added support for creating and destroying UE-specific TUN interfaces in SDAP.
- Refactored `nr_pdcp_module_init` to remove TUN-related logic and moved it
to SDAP.
- Updated NAS and SDAP layers to handle PDU session-specific TUN interface
creation and configuration.
- Enhanced SDAP entity management to include TUN socket handling and thread
lifecycle.
- Updated NAS message handling to initialize default PDU session TUN
interfaces in NOS1 mode.
- Use a single SDAP thread function for gNB and UE
- Allow noS1 mode also in SA on gNB
These changes improve modularity by isolating TUN interface management within
the SDAP layer, aligning with the 3GPP architecture, and simplifying the PDCP
layer.
Co-Authored-By: Robert Schmidt <robert.schmidt@openairinterface.org>
