fix: Fix the mtu when create network

Remove mtu if it is empty

If the mtu is empty, it should be removed
from the params of the request, otherwise it will cause
createing net error

Change-Id: I88f1d4398efd2ee70ab984d7598b04f8743c8d66

src/pages/network/containers/Network/actions/CreateNetwork.jsx

@@ -101,10 +101,13 @@ export class CreateNetwork extends ModalAction {
       name,
       description,
       availability_zone_hints: [availableZone],
-      mtu,
       port_security_enabled,
     };
 
+    if (mtu) {
+      networkCommonData.mtu = mtu;
+    }
+
     const networkAdminPageData = {
       'router:external': external_network,
       project_id,