calico: vxlan is the default for calico_network_backend (#8750)

Since https://github.com/kubernetes-sigs/kubespray/pull/8434

docs/calico.md

@@ -50,7 +50,7 @@ calico_datastore: kdd
 
 ### Optional : Define network backend
 
-In some cases you may want to define Calico network backend. Allowed values are `bird`, `vxlan` or `none`. Bird is a default value.
+In some cases you may want to define Calico network backend. Allowed values are `bird`, `vxlan` or `none`. `vxlan` is the default value.
 
 To re-define you need to edit the inventory and add a group variable `calico_network_backend`