OAI 5GC seems to have a bug, and occasionally might send a PDU session
setup request without having sent a UE context setup request, resulting
in no security context activated for a UE. This lead to an assertion in
rrc_gNB_process_e1_bearer_context_setup_resp().

To prevent the gNB from stopping, check if security is active before
triggering PDU sessions. If not, the gNB will reject PDU sessions.