API/USER: move _user_api_id to nas_user_t

openair3/NAS/UE/API/USER/user_api.c

openair3/NAS/UE/API/USER/user_api.h

openair3/NAS/UE/API/USER/user_api_defs.h

openair3/NAS/UE/API/USER/user_indication.c

openair3/NAS/UE/API/USER/user_indication.h

openair3/NAS/UE/EMM/IdleMode.c

openair3/NAS/UE/EMM/IdleMode.h

openair3/NAS/UE/EMM/SAP/EmmDeregisteredNoCellAvailable.c

openair3/NAS/UE/EMM/SAP/EmmDeregisteredPlmnSearch.c

openair3/NAS/UE/EMM/SAP/EmmRegisteredInitiated.c

openair3/NAS/UE/EMM/emm_main.c

openair3/NAS/UE/EMM/emm_main.h

openair3/NAS/UE/EMM/emm_proc.h

openair3/NAS/UE/ESM/DedicatedEpsBearerContextActivation.c

openair3/NAS/UE/ESM/DefaultEpsBearerContextActivation.c

openair3/NAS/UE/ESM/EpsBearerContextDeactivation.c

openair3/NAS/UE/ESM/esm_ebr.c

openair3/NAS/UE/ESM/esm_ebr.h

openair3/NAS/UE/ESM/esm_ebr_context.c

openair3/NAS/UE/UEprocess.c