dns: T5113: Support custom port for name-server forwarders

Support custom port for name-server forwarders that would allow using
custom ports in name server forwarders to enable forwarding to
alternative name servers (unbound, stubby, dnscrypt-proxy etc.)
operating on non-default port.

This would also allow using DNS Over TLS in PowerDNS Recursor 4.6 onwards
(pdns doesn't support certificate check for validity yet) by enabling
'dot-to-port-853'. This is set by default if compiled in with DoT support.
See: https://doc.powerdns.com/recursor/settings.html#dot-to-port-853

This also partially implements T921, T2195 (DoT without certificate check).

Implementation details:
- In 'dns/forwarding' configuration, 'name-server' now allows optional
  'port' (defaults to 53).
- Instead of modifying 'name-server-ipv4-ipv6.xml.i' to add optional
  'port', a new file 'name-server-ipv4-ipv6-port.xml.i' has been used
  to avoid impacting other places where it is reused because not all of
  them honor ports (mostly VPN related).
- The `host:port` entries to be used by PowerDNS recursor config are
  normalized eagerly at the point of loading VyOS `Config` instead of
  doing them lazily while rendering the Jinja2 template to keep the
  implementation less intrusive. The alternative would entail making
  quite a bit of change in how 'vyos-hostsd' processes 'static'
  'name_servers' entries or persists their runtime states.

1 files changed, 1 insertions, 1 deletions

diff --git a/interface-definitions/dns-forwarding.xml.in b/interface-definitions/dns-forwarding.xml.in
index 371f198c6..b23eaa351 100644
--- a/interface-definitions/dns-forwarding.xml.in
+++ b/interface-definitions/dns-forwarding.xml.in
@@ -635,7 +635,7 @@
                 </properties>
                 <defaultValue>1500</defaultValue>
               </leafNode>
-              #include <include/name-server-ipv4-ipv6.xml.i>
+              #include <include/name-server-ipv4-ipv6-port.xml.i>
               <leafNode name="source-address">
                 <properties>
                   <help>Local addresses from which to send DNS queries</help>