hcm: fix merge snafu with conflicting field numbers. (#486)

Signed-off-by: Harvey Tuch <htuch@google.com>

envoy/config/filter/network/http_connection_manager/v2/http_connection_manager.proto

@@ -19,6 +19,7 @@ import "gogoproto/gogo.proto";
 // [#protodoc-title: HTTP connection manager]
 // HTTP connection manager :ref:`configuration overview <config_http_conn_man>`.
 
+// [#comment:next free field: 21]
 message HttpConnectionManager {
   enum CodecType {
     option (gogoproto.goproto_enum_prefix) = false;
@@ -243,7 +244,7 @@ message HttpConnectionManager {
   // :ref:`http_connection_manager.represent_ipv4_remote_address_as_ipv4_mapped_ipv6
   // <config_http_conn_man_runtime_represent_ipv4_remote_address_as_ipv4_mapped_ipv6>` for runtime
   // control.
-  bool represent_ipv4_remote_address_as_ipv4_mapped_ipv6 = 19;
+  bool represent_ipv4_remote_address_as_ipv4_mapped_ipv6 = 20;
 }
 
 message Rds {