fix: prevent ack_q unbounded growth on duplicate packets

Check queue_find_data_by_index(ack_q) before creating a new ACK_PACKET
in ETCP_SECTION_PAYLOAD handler. Previously every duplicate packet
created a new entry in ack_q, and with links blocked (inf_block) the
queue grew without bounds.

src/etcp.c

@@ -1403,21 +1403,23 @@ void etcp_conn_input(struct ETCP_DGRAM* pkt) {
                             break;
                         }
                     }
-                    struct ACK_PACKET* p = (struct ACK_PACKET*)queue_entry_new_from_pool(etcp->instance->ack_pool);
-                    if (!p) {
-                        DEBUG_ERROR(DEBUG_CATEGORY_ETCP, "[%s] failed to allocate ACK_PACKET", etcp->log_name);
-                        len = 0;
-                        break;
-                    }
-                    p->seq=seq;
-                    p->pkt_timestamp=pkt->timestamp;
-                    p->recv_timestamp=get_current_timestamp();
-                    DEBUG_DEBUG(DEBUG_CATEGORY_ETCP, "[%s] RX add to ack_q seq=%d", etcp->log_name, seq);
-
-                    queue_data_put_with_index(etcp->ack_q, (struct ll_entry*)p);
-                    if (etcp->ack_resp_timer == NULL) {
-                        DEBUG_TRACE(DEBUG_CATEGORY_ETCP, "[%s] set ack_timer for delayed ACK send", etcp->log_name);
-                        etcp->ack_resp_timer = uasync_set_timeout(etcp->instance->ua, ACK_DELAY_TB, etcp, ack_response_timer_cb, "etcp_ack_resp");
+                    if (queue_find_data_by_index(etcp->ack_q, &seq) == NULL) {
+                        struct ACK_PACKET* p = (struct ACK_PACKET*)queue_entry_new_from_pool(etcp->instance->ack_pool);
+                        if (!p) {
+                            DEBUG_ERROR(DEBUG_CATEGORY_ETCP, "[%s] failed to allocate ACK_PACKET", etcp->log_name);
+                            len = 0;
+                            break;
+                        }
+                        p->seq=seq;
+                        p->pkt_timestamp=pkt->timestamp;
+                        p->recv_timestamp=get_current_timestamp();
+                        DEBUG_DEBUG(DEBUG_CATEGORY_ETCP, "[%s] RX add to ack_q seq=%d", etcp->log_name, seq);
+
+                        queue_data_put_with_index(etcp->ack_q, (struct ll_entry*)p);
+                        if (etcp->ack_resp_timer == NULL) {
+                            DEBUG_TRACE(DEBUG_CATEGORY_ETCP, "[%s] set ack_timer for delayed ACK send", etcp->log_name);
+                            etcp->ack_resp_timer = uasync_set_timeout(etcp->instance->ua, ACK_DELAY_TB, etcp, ack_response_timer_cb, "etcp_ack_resp");
+                        }
                     }
                     if (((int32_t)(etcp->last_delivered_id-seq)<0) && (queue_find_data_by_index(etcp->recv_q, &seq)==NULL)) {// проверяем есть ли пакет с этим seq
                         uint32_t pkt_len=len-5;