As previously pointed out in #9, the empty string is not generally a useful
value in the xDS APIs, so can be be considered equivalent to an unset
field. This is now documented in principles in #28 as well.
Also replace google.protobuf.BytesValue with bytes.
This will be useful for Google and other site specific extension of the
resolving of both names and ports. For listeners, ports and bound
addresses can be expressed in a site-specific format. For upstreams,
host names can be resolved using the plugin.
htuch
Piotr Sikora