When defining networkConfig inside install-config.yaml for a baremetal IPI deployment, users can specify the mtu field as a string (e.g., "1500").
Although this is valid YAML and passes openshift-install create manifests, it fails later when nmstatectl processes the generated config, because mtu must be an integer.
This leads to confusing runtime errors deep inside nmstate instead of failing early during installer validation.    

4.18.z    

    1. Create an install-config.yaml with a networkConfig section containing: 
       mtu: "1500"
     
    2. Run: openshift-install create manifests

    3. Validate the generated config with nmstatectl:
       nmstatectl gc test.yaml
     

Installer accepts mtu: "1500" without warning.
nmstatectl fails with error:

nm_wired_setting.props.mtu = setting.mtu
TypeError: expected int, got str    

Installer should validate mtu as an integer and reject string values.


openshift-install create manifests should fail early with a clear error message (e.g., mtu must be an integer, not a string).