Update comments and UT to remove /66 restriction

cmd/kubeadm/app/phases/controlplane/manifests.go

@@ -275,9 +275,6 @@ func getAPIServerCommand(cfg *kubeadmapi.MasterConfiguration) []string {
 // If the pod network size is /113 or larger, the node CIDR will be set to the same
 // size and this will be rejected later in validation.
 //
-// NOTE: Currently, the pod network must be /66 or larger. It is not reflected here,
-// but a smaller value will fail later validation.
-//
 // NOTE: Currently, the design allows a maximum of 64K nodes. This algorithm splits
 // the available bits to maximize the number used for nodes, but still have the node
 // CIDR be a multiple of eight.

cmd/kubeadm/app/phases/controlplane/manifests_test.go

@@ -823,15 +823,20 @@ func TestCalcNodeCidrSize(t *testing.T) {
 			expectedPrefix: "104",
 		},
 		{
-			name:           "V6: Largest subnet currently supported",
-			podSubnet:      "2001:db8::/66",
-			expectedPrefix: "80",
-		},
-		{
 			name:           "V6: For /64 pod net, use /80",
 			podSubnet:      "2001:db8::/64",
 			expectedPrefix: "80",
 		},
+		{
+			name:           "V6: For /48 pod net, use /64",
+			podSubnet:      "2001:db8::/48",
+			expectedPrefix: "64",
+		},
+		{
+			name:           "V6: For /32 pod net, use /48",
+			podSubnet:      "2001:db8::/32",
+			expectedPrefix: "48",
+		},
 	}
 	for _, test := range tests {
 		actualPrefix := calcNodeCidrSize(test.podSubnet)