roles/strongswan-swanctl: Load esp4 module at boot

The *esp4* kernel module does not load automatically on Fedora.  Without
this module, strongSwan can establish IKE SAs, but not ESP SAs.  Listing
the module name in a file in `/etc/modules-load.d` configures the
*systemd-modules-load* service to load it at boot.

roles/strongswan-swanctl/tasks/main.yml

@@ -5,6 +5,14 @@
   tags:
   - install
 
+- name: ensure esp4 module is configured to load at boot
+  copy:
+    src: esp4.modules-load.conf
+    dest: /etc/modules-load.d/esp4.conf
+    mode: '0644'
+  notify:
+  - load esp4 kernel module
+
 - name: ensure strongswan starts at boot
   service:
     name: strongswan