Fix macvlan private mode argument vaildation

Signed-off-by: Rony Weng <ronyweng@synology.com>

libnetwork/drivers/macvlan/macvlan_network.go

@@ -44,8 +44,8 @@ func (d *driver) CreateNetwork(nid string, option map[string]interface{}, nInfo
 	case "", modeBridge:
 		// default to macvlan bridge mode if -o macvlan_mode is empty
 		config.MacvlanMode = modeBridge
-	case modeOpt:
-		config.MacvlanMode = modeOpt
+	case modePrivate:
+		config.MacvlanMode = modePrivate
 	case modePassthru:
 		config.MacvlanMode = modePassthru
 	case modeVepa: