增加TCP Passthrough功能实现，调通明文转发流程。

platform/include/internal/tcp_stream.h

@@ -3,6 +3,13 @@
 #include <platform.h>
 
 struct tfe_stream * tfe_stream_create(struct tfe_proxy * pxy, struct tfe_thread_ctx * thread_ctx);
-void tfe_stream_init_by_fds(struct tfe_stream * stream, enum tfe_session_proto session_type,
-	evutil_socket_t fd_downstream, evutil_socket_t fd_upstream);
+
+enum tfe_stream_option
+{
+	TFE_STREAM_OPT_SESSION_TYPE,
+	TFE_STREAM_OPT_PASSTHROUGH
+};
+
+int tfe_stream_option_set(struct tfe_stream * stream, enum tfe_stream_option opt, const void * arg, size_t sz_arg);
+void tfe_stream_init_by_fds(struct tfe_stream * stream, evutil_socket_t fd_downstream, evutil_socket_t fd_upstream);
 void tfe_stream_destory(struct tfe_stream_private * stream);