PDCP build: exclude CU-CP/CU-UP from UE, guard E1 init for gNB only

- Common source in NR_PDCP_SRC and derive NR_PDCP_SRC_GNB (gNB) and
  NR_PDCP_SRC_UE from it; UE no longer compiles cucp_cuup_handler,
  cuup_cucp_if, cuup_cucp_direct, cuup_cucp_e1ap.
- NR_L2_SRC_UE uses NR_PDCP_SRC_UE so UE links only common PDCP sources.
- Add L2_NR compile definition PDCP_CUCP_CUUP; wrap nr_pdcp_e1_if_init
  call in nr_pdcp_oai_api.c with #ifdef PDCP_CUCP_CUUP so UE does not
  reference it.

UE build no longer depends on E1/CU-CP/CU-UP code or symbols; gNB
keeps full PDCP and E1 interface init.

Signed-off-by: Guido Casati <guido.casati@openairinterface.org>

CMakeLists.txt

@@ -1136,12 +1136,20 @@ set(NR_PDCP_SRC
   ${OPENAIR2_DIR}/LAYER2/nr_pdcp/nr_pdcp_integrity_nia2.c
   ${OPENAIR2_DIR}/LAYER2/nr_pdcp/nr_pdcp_integrity_nia1.c
   ${OPENAIR2_DIR}/LAYER2/nr_pdcp/asn1_utils.c
+  )
+
+# gNB: PDCP + CU-CP/CU-UP interface
+set(NR_PDCP_SRC_GNB
+  ${NR_PDCP_SRC}
   openair2/LAYER2/nr_pdcp/cucp_cuup_handler.c
   openair2/LAYER2/nr_pdcp/cuup_cucp_if.c
   openair2/LAYER2/nr_pdcp/cuup_cucp_direct.c
   openair2/LAYER2/nr_pdcp/cuup_cucp_e1ap.c
   )
 
+# UE build: PDCP only; CU-CP/CU-UP interface is gNB-only.
+set(NR_PDCP_SRC_UE ${NR_PDCP_SRC})
+
 set(NR_SDAP_SRC
   ${OPENAIR2_DIR}/SDAP/nr_sdap/nr_sdap.c
   ${OPENAIR2_DIR}/SDAP/nr_sdap/nr_sdap_entity.c
@@ -1185,7 +1193,7 @@ set(L2_LTE_SRC
   )
 
 set(L2_NR_SRC
-  ${NR_PDCP_SRC}
+  ${NR_PDCP_SRC_GNB}
   ${NR_SDAP_SRC}
   ${NR_RRC_DIR}/rrc_gNB.c
   ${NR_RRC_DIR}/mac_rrc_dl_direct.c
@@ -1221,7 +1229,7 @@ set(L2_RRC_SRC_UE
   )
 
 set(NR_L2_SRC_UE
-  ${NR_PDCP_SRC}
+  ${NR_PDCP_SRC_UE}
   ${NR_SDAP_SRC}
   ${NR_UE_RRC_DIR}/L2_interface_ue.c
   ${NR_UE_RRC_DIR}/main_ue.c
@@ -1365,6 +1373,7 @@ add_library(e1_if
 target_link_libraries(e1_if PRIVATE asn1_nr_rrc_hdrs asn1_lte_rrc_hdrs asn1_f1ap SECURITY ${OPENSSL_LIBRARIES} e1ap GTPV1U)
 
 target_link_libraries(L2_NR PRIVATE f1ap x2ap s1ap ngap nr_rrc e1ap nr_rlc nr_common)
+target_compile_definitions(L2_NR PRIVATE PDCP_CUCP_CUUP)
 if(OAI_AERIAL)
     target_compile_definitions(L2_NR PRIVATE ENABLE_AERIAL)
 endif()
@@ -1898,7 +1907,7 @@ add_executable(nr-cuup
   executables/nr-cuup.c
   ${NR_RRC_DIR}/rrc_gNB_UE_context.c
   ${OPENAIR2_DIR}/E1AP/e1ap_setup.c
-  ${NR_PDCP_SRC}
+  ${NR_PDCP_SRC_GNB}
   ${NR_SDAP_SRC}
   )
 
@@ -1909,6 +1918,7 @@ target_link_libraries(nr-cuup PRIVATE
                       alg
                       dl pthread ${T_LIB})
 target_link_libraries(nr-cuup PRIVATE asn1_lte_rrc_hdrs asn1_nr_rrc_hdrs)
+target_compile_definitions(nr-cuup PRIVATE PDCP_CUCP_CUUP)
 if(E2_AGENT)
   target_link_libraries(nr-cuup PRIVATE e2_agent e2_agent_arg e2_ran_func_cuup)
   target_compile_definitions(nr-cuup PRIVATE ${E2AP_VERSION} ${KPM_VERSION} E2_AGENT)