(netflow) fix missing check for egress_only

src/opnsense/service/templates/OPNsense/Netflow/netflow.conf

@@ -15,11 +15,11 @@ netflow_interfaces="{% for interface in OPNsense.Netflow.capture.interfaces.spli
     physical_interface(interface)
 }} {%
   endfor%}"
-netflow_egress_only="{% for interface in OPNsense.Netflow.capture.egress_only.split(',')
+netflow_egress_only="{% if OPNsense.Netflow.capture.egress_only %}{% for interface in OPNsense.Netflow.capture.egress_only.split(',')
 %}{{
     physical_interface(interface)
-}} {%
-  endfor%}"
+}}{%
+  endfor%} {%endif%}"
 netflow_version="{%if OPNsense.Netflow.capture.version == 'v9' %}9{% else %}5{%endif%}"
 netflow_int_destination="127.0.0.1:2055"
 netflow_destinations="{{OPNsense.Netflow.capture.targets.replace(',', ' ')}}"