improve hole punching and stun test (#124)

* implement new stun test algorithm, do test faster and provide more info
* support punching for symmetric

easytier/src/common/netns.rs

@@ -75,7 +75,7 @@ impl NetNSGuard {
     }
 }
 
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 pub struct NetNS {
     name: Option<String>,
 }