perNodeHostBits defines the number of host bits to be configured per node.
A subnet mask determines how much of the address is used for network bits and host bits.
For example an IPv4 address of 192.168.0.0/24, splits the address into 24 bits for the network portion and 8 bits for the host portion.
To allocate 256 IPs, set this field to 8 (a /24 mask for IPv4 or a /120 for IPv6).
Minimum value is 4 (16 IPs).
This field is immutable.
ClusterCIDRSpec defines the desired state of ClusterCIDR.