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

@@ -1403,6 +1403,7 @@ void etcp_conn_input(struct ETCP_DGRAM* pkt) {
                             break;
                         }
                     }
+                    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);
@@ -1419,6 +1420,7 @@ void etcp_conn_input(struct ETCP_DGRAM* pkt) {
                             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;
                         DEBUG_TRACE(DEBUG_CATEGORY_ETCP, "[%s] adding packet seq=%u to recv_q (last_delivered_id=%u)", etcp->log_name, seq, etcp->last_delivered_id);