add vtun listener and handler

handler/vtun/metadata.go

@@ -0,0 +1,12 @@
+package tun
+
+import (
+	mdata "github.com/go-gost/core/metadata"
+)
+
+type metadata struct {
+}
+
+func (h *tunHandler) parseMetadata(md mdata.Metadata) (err error) {
+	return
+}