Currently, there is only one interface to set ctlplaneNetmask, it is setting the paramter in `OpenStackDataPlaneNodeSet` CR.

  baremetalSetTemplate:
    deploymentSSHSecret: dataplane-ansible-ssh-private-key-secret
    bmhNamespace: openshift-machine-api
    cloudUserName: cloud-admin
    bmhLabelSelector:
      app: openstack
    ctlplaneInterface: enp1s0
    ctlplaneNetmask: 23
    dnsSearchDomains:
      - osptest.openstack.org

Without the assignment, ctlplaneNetmask is 24 by default.
It causes a trouble when ctlplane network is not 24 bit netmask.
Also, we don't have any document to assign the value in our doc.

Additionally, explicit definition to netmask is not reasonable because other parameters, IP address, gateway are retrieved from IPAM.
So, ctlplaneNetmask should be taken from IPAM also.