Fix the boolean that manages the network interfaces settings.

library/roles/postfix/templates/main.cf.j2

@@ -72,12 +72,13 @@ myorigin = {{ ansible_fqdn }}
 #
 # Note: you need to stop/start Postfix when this parameter changes.
 #
-{% if not postfix_use_inet_interfaces %}
+{% if postfix_use_inet_interfaces %}
 {% if not postfix_smtpd_server %}
 inet_interfaces = localhost
 inet_protocols = ipv4
 {% else %}
 inet_interfaces = {% for int in postfix_inet_interfaces %}{{ int }}{% if not loop.last %}, {% endif %}{% endfor %}
+
 inet_protocols = {% for proto in postfix_inet_protocols %}{{ proto }}{% if not loop.last %}, {% endif %}{% endfor %}
 {% endif %}
 {% endif %}