T75: migrate from pmacct to ipt_NETFLOW

* Change nft to iptables in system_flow-accounting.py as ipt_NETFLOW
  is iptales plugin
* Remove specific and non-relevant pmacct options
* Add ipt_NETFLOW options
* Move 'interfaces' to 'netflow' tree
* Support more flexible 'source-address' and 'source-interface' for
  each server instead of one source
* Add migration script
* Update op mode command 'show flow-accounting'

Author: hedrok

data/templates/ipt-netflow/ipt_NETFLOW.conf.j2

@@ -0,0 +1,29 @@
+{% if netflow.engine_id is vyos_defined %}
+options ipt_NETFLOW engine-id={{ netflow.engine_id }}
+{% endif %}
+{% if netflow.max_flows is vyos_defined %}
+options ipt_NETFLOW maxflows={{ netflow.max_flows }}
+{% endif %}
+{% if netflow.sampling_rate is vyos_defined %}
+options ipt_NETFLOW sampler=random:{{ netflow.sampling_rate }}
+{% endif %}
+{% if netflow.server is vyos_defined %}
+{%     set servers_list = [] %}
+{%     for server in netflow.server %}
+{%         set d = netflow.server[server] %}
+{%         set s = (server | bracketize_ipv6) ~ ':' ~ d['port'] %}
+{%         set s = s ~ ('%' ~ d['source_interface'] if d['source_interface'] is vyos_defined else '') %}
+{%         set s = s ~ ('@' ~ d['source_address'] if d['source_address'] is vyos_defined else '') %}
+{%         set _ = servers_list.append(s) %}
+{%     endfor %}
+options ipt_NETFLOW destination={{ servers_list | join(",") }}
+{% endif %}
+{% if netflow.version is vyos_defined %}
+options ipt_NETFLOW protocol={{ netflow.version }}
+{% endif %}
+{% if netflow.inactive_timeout is vyos_defined %}
+options ipt_NETFLOW inactive_timeout={{ netflow.inactive_timeout }}
+{% endif %}
+{% if netflow.active_timeout is vyos_defined %}
+options ipt_NETFLOW active_timeout={{ netflow.active_timeout }}
+{% endif %}

data/templates/pmacct/override.conf.j2

@@ -318,9 +318,6 @@ Depends:
 # For "vpn openconnect"
   ocserv,
 # End "vpn openconnect"
-# For "system flow-accounting"
-  pmacct (>= 1.6.0),
-# End "system flow-accounting"
 # For "system syslog"
   rsyslog,
 # End "system syslog"

data/templates/pmacct/uacctd.conf.j2

@@ -1,3 +1,3 @@
 <!-- include start from include/version/flow-accounting-version.xml.i -->
-<syntaxVersion component='flow-accounting' version='2'></syntaxVersion>
+<syntaxVersion component='flow-accounting' version='3'></syntaxVersion>
 <!-- include end -->