20.16.

$ oc patch networks.operator.openshift.io cluster --type=merge \
  -p '{
    "spec":{
      "defaultNetwork":{
        "ovnKubernetesConfig":{
          "hybridOverlayConfig":{
            "hybridClusterNetwork":[
              {
                "cidr": "<cidr>",
                "hostPrefix": <prefix>
              }
            ],
            "hybridOverlayVXLANPort": <overlay_port>
          }
        }
      }
    }
  }'

network.operator.openshift.io/cluster patched

$ oc get network.operator.openshift.io -o jsonpath="{.items[0].spec.defaultNetwork.ovnKubernetesConfig}"