Refactor DNS relay

- Allow working in standalone mode
- Use same UDP socket for sending response packet
- Send TCP queries with ProxyStream directly

ref #213

tests/socks5.rs

@@ -39,7 +39,7 @@ impl Socks5TestServer {
             },
             cli_config: {
                 let mut cfg = Config::new(ConfigType::Socks5Local);
-                cfg.local = Some(ServerAddr::from(local_addr));
+                cfg.local_addr = Some(ServerAddr::from(local_addr));
                 cfg.server = vec![ServerConfig::basic(svr_addr, pwd.to_owned(), method)];
                 cfg.mode = if enable_udp { Mode::TcpAndUdp } else { Mode::TcpOnly };
                 cfg

tests/udp.rs

@@ -46,7 +46,7 @@ fn get_svr_config() -> Config {
 
 fn get_cli_config() -> Config {
     let mut cfg = Config::new(ConfigType::Socks5Local);
-    cfg.local = Some(LOCAL_ADDR.parse().unwrap());
+    cfg.local_addr = Some(LOCAL_ADDR.parse().unwrap());
     cfg.server = vec![ServerConfig::basic(
         SERVER_ADDR.parse().unwrap(),
         PASSWORD.to_owned(),