bugfix: fix PCDP inst (again)

This commit follows 7d9945e884.

lte-softmodem UE in S1 and lte-softmodem UE in noS1 modes behave
differently here.

This commit fixes the issue for thoses cases.

Other cases (eNB S1, eNB noS1, oaisim S1/noS1) have to be checked.

openair2/LAYER2/PDCP_v10.1.0/pdcp.c

@@ -817,8 +817,13 @@ pdcp_data_ind(
 #if defined(OAI_EMU)
         ((pdcp_data_ind_header_t*) new_sdu_p->data)->inst  = ctxt_pP->module_id + oai_emulation.info.nb_enb_local - oai_emulation.info.first_ue_local;
 #else
-        /* TODO: inst is 1 for the UE or do we keep 0? Seems to be 1 but not sure */
+#  if defined(ENABLE_USE_MME)
+        /* for the UE compiled in S1 mode, we need 1 here
+         * for the UE compiled in noS1 mode, we need 0
+         * TODO: be sure of this
+         */
         ((pdcp_data_ind_header_t*) new_sdu_p->data)->inst  = 1;
+#  endif
 #endif
       } else {
         ((pdcp_data_ind_header_t*) new_sdu_p->data)->rb_id = rb_id + (ctxt_pP->module_id * maxDRB);