[~] 修复anti_amplification_limit设小不生效的问题 (#451)

* [~] 修复anti amplification设小不生效的问题;

* [～] 修改demo默认值为4

* [=] 合并主干版本

Author: Yanmei-Liu

demo/demo_server.c

@@ -1525,7 +1525,7 @@ xqc_demo_svr_init_conn_settings(xqc_engine_t *engine, xqc_demo_svr_args_t *args)
         .is_interop_mode = args->quic_cfg.is_interop_mode,
         .max_pkt_out_size = args->quic_cfg.max_pkt_sz,
         .adaptive_ack_frequency = 1,
-        .anti_amplification_limit = 3,
+        .anti_amplification_limit = 4,
     };
 
     xqc_server_set_conn_settings(engine, &conn_settings);

src/transport/xqc_conn.c

@@ -175,7 +175,8 @@ xqc_server_set_conn_settings(xqc_engine_t *engine, const xqc_conn_settings_t *se
         engine->default_conn_settings.idle_time_out = settings->idle_time_out;
     }
 
-    if (settings->anti_amplification_limit > XQC_DEFAULT_ANTI_AMPLIFICATION_LIMIT) {
+    /* default value: 5x, it could be set to meet application need */
+    if (settings->anti_amplification_limit > 0) {
         engine->default_conn_settings.anti_amplification_limit = settings->anti_amplification_limit;
     }
 
@@ -692,7 +693,7 @@ xqc_conn_create(xqc_engine_t *engine, xqc_cid_t *dcid, xqc_cid_t *scid,
         xc->conn_settings.idle_time_out = XQC_CONN_DEFAULT_IDLE_TIMEOUT;
     }
 
-    if (xc->conn_settings.anti_amplification_limit < XQC_DEFAULT_ANTI_AMPLIFICATION_LIMIT) {
+    if (xc->conn_settings.anti_amplification_limit == 0) {
         xc->conn_settings.anti_amplification_limit = XQC_DEFAULT_ANTI_AMPLIFICATION_LIMIT;
     }