Stabilize test_dscp_to_queue_mapping (sonic-net#21340)

1. To mitigate the impact of noise packets, flush the PTF dataplane before sending and verifying packets
2. Increase the timeout in case ptf can not handle all packet in the buffer during 1 second, the ptf buffer has a lot of packets

Signed-off-by: Saravanan <saravanan@nexthop.ai>

Author: JibinBao

tests/qos/test_qos_dscp_mapping.py

@@ -188,14 +188,14 @@ def send_and_verify_traffic(ptfadapter,
     """
     pkt_egress_index = 0
     ptf_dst_port_list = []
-    ptfadapter.dataplane.flush()
     logger.info("Send packet(s) from port {} from downstream to upstream".format(ptf_src_port_id))
 
     try:
         for pkt, exp_pkt in zip(pkt_list, exp_pkt_list):
+            ptfadapter.dataplane.flush()
             testutils.send(ptfadapter, ptf_src_port_id, pkt, count=DEFAULT_PKT_COUNT)
             logger.info(f"Send packet: {pkt}, expected packet: {exp_pkt}")
-            result = testutils.verify_packet_any_port(ptfadapter, exp_pkt, ports=ptf_dst_port_ids, timeout=1)
+            result = testutils.verify_packet_any_port(ptfadapter, exp_pkt, ports=ptf_dst_port_ids, timeout=5)
             if isinstance(result, bool):
                 logger.info("Return a dummy value for VS platform")
                 port_index = 0
@@ -493,7 +493,8 @@ def test_dscp_to_queue_mapping(self, ptfadapter, rand_selected_dut, localhost, d
         with allure.step("Run test"):
             self._run_test(ptfadapter, duthost, tbinfo, test_params, inner_dst_ip_list, dut_qos_maps_module, dscp_mode)
 
-        if completeness_level != "basic":
+        if completeness_level != "basic" and \
+                not duthost.dut_basic_facts()['ansible_facts']['dut_basic_facts'].get("is_smartswitch"):
             with allure.step("Do warm-reboot"):
                 reboot(duthost, localhost, reboot_type="warm", safe_reboot=True, check_intf_up_ports=True,
                        wait_warmboot_finalizer=True)