fix var name

linux/nftables/templates/nftables.conf

@@ -33,7 +33,7 @@ table inet firewall {
 
         {% if nftables_external_interfaces is defined %}
         {% for interface in ansible_interfaces %}
-        {% if interface not in nftables_blacklisted_interfaces %}
+        {% if interface not in nftables_external_interfaces %}
         iifname {{ interface }} accept
         {% endif %}
         {% endfor %}