[sonic-swss] test case of test_dpb_arp_flush in test_port_dpb_system.py are failing randomly

[AshokDaparthi]

Hi,

When we raise pull requests to sonic-utilities and soni-swss. We see random " vstest" unit test case failing in multiple PR's.
Most of the test case is related to test_dpb_arp_flush scenario.

Example:
1#
sonic-net/sonic-utilities#1640
Log:
https://dev.azure.com/mssonic/build/_build/results?buildId=16610&view=logs&j=3f6395b2-1619-5ebe-f305-2aedcf353cb5&t=35460df8-21be-5313-3ee4-50900c6db765&l=1203

2#
sonic-net/sonic-utilities#1626
Log:
https://dev.azure.com/mssonic/build/_build/results?buildId=17906&view=logs&j=3f6395b2-1619-5ebe-f305-2aedcf353cb5&t=35460df8-21be-5313-3ee4-50900c6db765&l=1093

Fail Logs:
test_dpb_arp_flush_on_port_oper_shut failed (1 runs remaining out of 2).
<class 'AssertionError'>
Unexpected number of keys: expected=3, received=2 (('oid:0x60000000010f1', 'oid:0x60000000005a7')), table="ASIC_STATE:SAI_OBJECT_TYPE_ROUTER_INTERFACE"
[<TracebackEntry /home/vsts/work/1/sonic-swss/tests/test_port_dpb_system.py:761>, <TracebackEntry /home/vsts/work/1/sonic-swss/tests/test_port_dpb_system.py:39>, <TracebackEntry /home/vsts/work/1/sonic-swss/tests/dvslib/dvs_database.py:366>]
test_dpb_arp_flush_on_port_oper_shut failed; it passed 0 out of the required 1 times.
<class 'AssertionError'>
Unexpected number of keys: expected=3, received=2 (('oid:0x60000000010f1', 'oid:0x60000000005a7')), table="ASIC_STATE:SAI_OBJECT_TYPE_ROUTER_INTERFACE"
[<TracebackEntry /home/vsts/work/1/sonic-swss/tests/test_port_dpb_system.py:761>, <TracebackEntry /home/vsts/work/1/sonic-swss/tests/test_port_dpb_system.py:39>, <TracebackEntry /home/vsts/work/1/sonic-swss/tests/dvslib/dvs_database.py:366>]
test_dpb_arp_flush_on_vlan_member_remove failed (1 runs remaining out of 2).
<class 'AssertionError'>
Unexpected number of keys: expected=3, received=2 (('oid:0x60000000010f1', 'oid:0x60000000005a7')), table="ASIC_STATE:SAI_OBJECT_TYPE_ROUTER_INTERFACE"
[<TracebackEntry /home/vsts/work/1/sonic-swss/tests/test_port_dpb_system.py:825>, <TracebackEntry /h

[zhangyanzhao]

@zhenggen-xu please help to take a look.