network_facts: streamline set_fact and setup calls

- invoke setup module only once to gather ipv4 and ipv6 addresses
- eliminate remaining use of `fallback_ip` and `fallback_ip6`, allowing
  us to define (with `set_fact` all the "computed" IPs variable in one
  go, since there is no longer a dependency between them.

roles/kubernetes/control-plane/tasks/check-api.yml

@@ -1,7 +1,7 @@
 ---
 - name: Kubeadm | Check api is up
   uri:
-    url: "https://{{ ip | default(fallback_ip) }}:{{ kube_apiserver_port }}/healthz"
+    url: "https://{{ main_ip | ansible.utils.ipwrap }}:{{ kube_apiserver_port }}/healthz"
     validate_certs: false
   when: ('kube_control_plane' in group_names)
   register: _result