feat: Use MAC address provided by nerdctl

The nerdctl `--mac-address` command line passes the address to the CNI
plugin with the `MAC` arg.

See `getCNINamespaceOpts`:
https://github.com/containerd/nerdctl/blob/main/pkg/containerutil/container_network_manager_windows.go#L184-L186

cni/cni.go

@@ -105,6 +105,11 @@ type K8SPodEnvArgs struct {
 	K8S_POD_INFRA_CONTAINER_ID cniTypes.UnmarshallableString `json:"K8S_POD_INFRA_CONTAINER_ID,omitempty"`
 }
 
+type EndpointArgs struct {
+	cniTypes.CommonArgs
+	MAC cniTypes.UnmarshallableString
+}
+
 type OptionalFlags struct {
 	LocalRoutePortMapping       bool `json:"localRoutedPortMapping"`
 	AllowAclPortMapping         bool `json:"allowAclPortMapping"`
@@ -194,6 +199,17 @@ func ParseCniArgs(args string) (*K8SPodEnvArgs, error) {
 	return &podConfig, nil
 }
 
+// ParseCniEndpointArgs
+func ParseCniEndpointArgs(args string) (*EndpointArgs, error) {
+	epArgs := EndpointArgs{}
+	err := cniTypes.LoadArgs(args, &epArgs)
+	if err != nil {
+		return nil, err
+	}
+
+	return &epArgs, nil
+}
+
 // Serialize marshals a network configuration to bytes.
 func (config *NetworkConfig) Serialize() []byte {
 	bytes, _ := json.Marshal(config)

common/core/network.go

@@ -105,6 +105,12 @@ func (plugin *netPlugin) Add(args *cniSkel.CmdArgs) (resultError error) {
 		k8sNamespace = string(podConfig.K8S_POD_NAMESPACE)
 	}
 
+	epConfig, err := cni.ParseCniEndpointArgs(args.Args)
+	if err != nil {
+		logrus.Errorf("[cni-net] Failed to parse endpoint args, err:%v", err)
+		return err
+	}
+
 	// Parse network configuration from stdin.
 	cniConfig, err := cni.ParseNetworkConfig(args.StdinData)
 	if err != nil {
@@ -133,6 +139,15 @@ func (plugin *netPlugin) Add(args *cniSkel.CmdArgs) (resultError error) {
 		return err
 	}
 
+	if epConfig.MAC != "" {
+		hwAddr, err := net.ParseMAC(string(epConfig.MAC))
+		if err != nil {
+			logrus.Errorf("[cni-net] Failed to parse MAC addres '%s', err:%v", epConfig.MAC, err)
+			return err
+		}
+
+		epInfo.MacAddress = hwAddr
+	}
 	epInfo.DualStack = cniConfig.OptionalFlags.EnableDualStack
 
 	// Check for missing namespace