Hi Laurent,
You can modify the preferred NDMP LIF role using:
cluster1::> vserver services ndmp modify -vserver vserver1 -preferred-interface-role {cluster|data|node-mgmt|intercluster|cluster-mgmt}, ... ] Preferred Interface Role
Also assume you've checked your configuration as per the documentation below:
https://library.netapp.com/ecmdocs/ECMP12366513/html/GUID-B9E37D91-05A7-4AC9-BDDD-24AB7A7DED50.html
https://library.netapp.com/ecmdocs/ECMP12366513/html/GUID-932EC20E-B0CB-4626-B57F-8A26AEAC90CA.html
/Matt