e1: change security settings only if parameters present

If the Bearer Context Modification Request does not contain security
information, the PDCP entity shall keep the currently configured security
settings.

Passing -1 for ciphering_algorithm and integrity_algorithm is the way
to implement this logic.

openair2/LAYER2/nr_pdcp/cucp_cuup_handler.c

@@ -279,6 +279,10 @@ void e1_bearer_context_modif(const e1ap_bearer_mod_req_t *req)
           security_parameters.integrity_algorithm = req->secInfo->integrityProtectionAlgorithm;
           memcpy(security_parameters.ciphering_key, req->secInfo->encryptionKey, NR_K_KEY_SIZE);
           memcpy(security_parameters.integrity_key, req->secInfo->integrityProtectionKey, NR_K_KEY_SIZE);
+        } else {
+          /* don't change security settings if not present in the Bearer Context Modification Request */
+          security_parameters.ciphering_algorithm = -1;
+          security_parameters.integrity_algorithm = -1;
         }
         nr_pdcp_reestablishment(req->gNB_cu_up_ue_id,
                                 to_modif->id,