change SNI domains to SNI domain names, explain the wildcard prefix (#3372)

Signed-off-by: Vadim Eisenberg <vadime@il.ibm.com>

Mirrored from https://github.com/envoyproxy/envoy @ cd1cd040abcd0c8b26146be3337f228b0f28fa95

envoy/api/v2/listener/listener.proto

@@ -48,8 +48,11 @@ message Filter {
 // Specifies the match criteria for selecting a specific filter chain for a
 // listener.
 message FilterChainMatch {
-  // If non-empty, the SNI domains to consider. May contain a wildcard prefix,
+  // If non-empty, the SNI domain names to consider. May contain a wildcard prefix for
-  // e.g. ``*.example.com``.
+  // the bottom-level domain of a domain name, e.g. ``*.example.com``. Note that
+  // ``foo.example.com`` will be matched by ``foo.example.com`` and ``*.example.com``
+  // SNI domain names, but **not** by ``*foo.example.com``, ``*oo.example.com``,
+  // ``*example.com``, ``*.com`` or ``*``.
   //
   // .. attention::
   //