r/collectd: Max unixsock plugin optional

Some hosts may not need this plugin, or may not have it installed.
Notably, it is not needed or used on my systems based on Buildroot,
since the only current use case for it is to keep track of the Fedora
version.

roles/collectd/defaults/main.yml

@@ -14,4 +14,5 @@ collectd_plugins_defaults:
 
 collectd_df: {}
 
+collectd_unixsock_plugin: true
 collectd_load_unixsock_plugin: true

roles/collectd/templates/collectd-unixsock.conf.j2

@@ -1,3 +1,4 @@
+{% if collectd_unixsock_plugin %}
 {% if collectd_load_unixsock_plugin %}
 LoadPlugin unixsock
 {% endif %}
@@ -16,3 +17,4 @@ LoadPlugin unixsock
     DeleteSocket false
 {% endif %}
 </Plugin>
+{% endif %}