feat: allow using --proxy-forward-by-system together with --enable-exit-node (#957)

easytier/src/instance/instance.rs

@@ -71,7 +71,6 @@ impl IpProxy {
 
     async fn start(&self) -> Result<(), Error> {
         if (self.global_ctx.get_proxy_cidrs().is_empty()
-            || self.global_ctx.proxy_forward_by_system()
             || self.started.load(Ordering::Relaxed))
             && !self.global_ctx.enable_exit_node()
             && !self.global_ctx.no_tun()
@@ -79,6 +78,13 @@ impl IpProxy {
             return Ok(());
         }
 
+        // Actually, if this node is enabled as an exit node,
+        // we still can use the system stack to forward packets.
+        if self.global_ctx.proxy_forward_by_system()
+          && !self.global_ctx.no_tun() {
+            return Ok(());
+        }
+
         self.started.store(true, Ordering::Relaxed);
         self.tcp_proxy.start(true).await?;
         if let Err(e) = self.icmp_proxy.start().await {