port forward (#736)

* support tcp port forward
* support udp port forward
* command line option for port forward

easytier/src/proto/common.proto

@@ -155,3 +155,14 @@ message PeerFeatureFlag {
   bool kcp_input = 3;
   bool no_relay_kcp  = 4;
 }
+
+enum SocketType {
+  TCP = 0;
+  UDP = 1;
+}
+
+message PortForwardConfigPb {
+    SocketAddr bind_addr = 1;
+    SocketAddr dst_addr = 2;
+    SocketType socket_type = 3;
+}