Preserve backwards compatibility of CreateNetworkStatus

The CNI spec - [0] - states that the `sandbox` attribute in the CNI result
should be used to represent:
```
The isolation domain reference (e.g. path to network namespace) for the
interface, or empty if on the host. For interfaces created inside the container,
this should be the value passed via CNI_NETNS
```

Some CNIs (like calico) do **not** set the sandbox for their interfaces
(below you'll find an example of a cached CNI result created by calico
CNI):
```
{
  ...
  "result": {
    "cniVersion": "0.3.1",
    "dns": {},
    "interfaces": [
      {
        "name": "cali05f4a1849c5"
      }
    ],
    "ips": [
      {
        "address": "10.244.196.152/32",
        "version": "4"
      },
      {
        "address": "fd10:244::c497/128",
        "version": "6"
      }
    ]
  }
}
```

Thus, when multus started to use `CreateNetworkStatuses` (plural) we
broke calico users relying on the network-status annotations (since that
function relies on the sandbox attribute being defined to identify
container interfaces).

This commit changes the code to use the original status creation
whenever `CreateNetworkStatuses` is created with a single interface,
thus ensuring the original behavior will be provided to user. Unit tests
are also added.

[0] - https://github.com/containernetworking/cni/blob/main/SPEC.md#add-success

Signed-off-by: Miguel Duarte Barroso <[email protected]>

pkg/utils/net-attach-def.go

@@ -136,6 +136,11 @@ func CreateNetworkStatuses(r cnitypes.Result, networkName string, defaultNetwork
 		return nil, fmt.Errorf("error converting the type.Result to cni100.Result: %v", err)
 	}
 
+	if len(result.Interfaces) == 1 {
+		networkStatus, err := CreateNetworkStatus(r, networkName, defaultNetwork, dev)
+		return []*v1.NetworkStatus{networkStatus}, err
+	}
+
 	// Discover default routes upfront and reuse them if necessary.
 	var useDefaultRoute []string
 	for _, route := range result.Routes {

pkg/utils/net-attach-def_test.go

@@ -337,6 +337,48 @@ var _ = Describe("Netwok Attachment Definition manipulations", func() {
 		})
 	})
 
+	Context("create network statuses for a single interface which omits the sandbox info", func() {
+		var cniResult *cni100.Result
+
+		BeforeEach(func() {
+			cniResult = &cni100.Result{
+				CNIVersion: "1.1.0",
+				Interfaces: []*cni100.Interface{
+					{
+						Name: "foo",
+					},
+				},
+				IPs: []*cni100.IPConfig{
+					{
+						Address: *EnsureCIDR("10.244.196.152/32"),
+					},
+					{
+						Address: *EnsureCIDR("fd10:244::c497/128"),
+					},
+				},
+			}
+		})
+
+		It("creates network statuses with a single entry", func() {
+			networkStatuses, err := CreateNetworkStatuses(cniResult, "test-default-net-without-sandbox", true, nil)
+			Expect(err).NotTo(HaveOccurred())
+
+			Expect(networkStatuses).To(WithTransform(
+				func(status []*v1.NetworkStatus) []*v1.NetworkStatus {
+					for i := range status {
+						status[i].DNS = v1.DNS{}
+					}
+					return status
+				}, ConsistOf(
+					&v1.NetworkStatus{
+						Name:    "test-default-net-without-sandbox",
+						IPs:     []string{"10.244.196.152", "fd10:244::c497"},
+						Default: true,
+					},
+				)))
+		})
+	})
+
 	It("parse network selection element in pod", func() {
 		selectionElement := `
 		[{