docs: release note and unhide transparent LDS field (#593)

Signed-off-by: Romain Lenglet <romain@covalent.io>

docs/root/configuration/listener_filters/original_dst_filter.rst

@@ -4,10 +4,11 @@ Original Destination
 ====================
 
 Original destination listener filter reads the SO_ORIGINAL_DST socket option set when a connection
-has been redirected by iptables REDIRECT. Later processing in Envoy sees the restored destination
-address as the connection's local address, rather than the address at which the listener is
-listening at. Furthermore, :ref:`an original destination cluster
-<arch_overview_service_discovery_types_original_destination>` may be used to forward HTTP requests
-or TCP connections to the restored destination address.
+has been redirected by an iptables REDIRECT target, or by an iptables TPROXY target in combination
+with setting the listener's :ref:`transparent <envoy_api_field_Listener.transparent>` option.
+Later processing in Envoy sees the restored destination address as the connection's local address,
+rather than the address at which the listener is listening at. Furthermore, :ref:`an original
+destination cluster <arch_overview_service_discovery_types_original_destination>` may be used to
+forward HTTP requests or TCP connections to the restored destination address.
 
 * :ref:`v2 API reference <envoy_api_field_listener.Filter.name>`

docs/root/intro/version_history.rst

@@ -17,6 +17,8 @@ Version history
 * logger: all :ref:`logging levels <operations_admin_interface_logging>` can be configured
   at run-time: trace debug info warning error critical.
 * logger: added the ability to optionally set the log format via the :option:`--log-format` option.
+* sockets: added `IP_TRANSPARENT` socket option support for :ref:`listeners
+  <envoy_api_field_Listener.transparent>`.
 * sockets: added `IP_FREEBIND` socket option support for :ref:`listeners
   <envoy_api_field_Listener.freebind>` and upstream connections via
   :ref:`cluster manager wide

envoy/api/v2/lds.proto

@@ -127,7 +127,6 @@ message Listener {
   // before a connection is created.
   repeated listener.ListenerFilter listener_filters = 9 [(gogoproto.nullable) = false];
 
-  // [#not-implemented-hide:]
   // Whether the listener should be set as a transparent socket.
   // When this flag is set to true, connections can be redirected to the listener using an
   // *iptables* *TPROXY* target, in which case the original source and destination addresses and