Fix the QOS test failure when packet sent are greater than 4K in size

tests/qos/qos_sai_base.py

@@ -132,6 +132,7 @@ def runPtfTest(self, ptfhost, testCase='', testParams={}, relax=False):
             is_python3=True,
             relax=relax,
             timeout=1200,
+            socket_recv_size=16384,
             custom_options=custom_options
         )