The LLSK socket is an interface allowing thid-parties to implement and
hook their RLC/MAC/RRC stack to osmo-hnodbe, which takes care of
interconnection with the rest of the RAN and core network (Iuh, RTP,
GTP-U, etc.).
Related: SYS#5516
Change-Id: Icaabb2206d6f141d4fba47dedf71f8ec37e6257d
