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/mod.rs

@@ -8,6 +8,7 @@ use tracing::Instrument;
 
 pub mod config;
 pub mod constants;
+pub mod defer;
 pub mod error;
 pub mod global_ctx;
 pub mod ifcfg;