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

@@ -274,10 +274,16 @@ void e1_bearer_context_modif(const e1ap_bearer_mod_req_t *req)
 
       if (to_modif->pdcp_config.pDCP_Reestablishment) {
         nr_pdcp_entity_security_keys_and_algos_t security_parameters;
-        security_parameters.ciphering_algorithm = req->cipheringAlgorithm;
-        security_parameters.integrity_algorithm = req->integrityProtectionAlgorithm;
-        memcpy(security_parameters.ciphering_key, req->encryptionKey, NR_K_KEY_SIZE);
-        memcpy(security_parameters.integrity_key, req->integrityProtectionKey, NR_K_KEY_SIZE);
+        if (req->has_security_information) {
+          security_parameters.ciphering_algorithm = req->cipheringAlgorithm;
+          security_parameters.integrity_algorithm = req->integrityProtectionAlgorithm;
+          memcpy(security_parameters.ciphering_key, req->encryptionKey, NR_K_KEY_SIZE);
+          memcpy(security_parameters.integrity_key, req->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,
                                 false,