Fix show interface counters for Chassis Packet Supervisor (sonic-net#3734)

What I did
On Chassis-packet supervisor, show interface counter -d all returns no data

How I did it
Fixed the condition in portstat.py to use right path for Chassis Packet RP to collect counters.
Added condition to collect link state information.

How to verify it
Run 'show interface counters -d all' on Chassis-Packet Supervisor

Author: anamehra

scripts/portstat

@@ -27,7 +27,11 @@ try:
             import sonic_py_common
             from swsscommon.swsscommon import SonicV2Connector
             sonic_py_common.device_info.is_supervisor = mock.MagicMock(return_value=True)
-            sonic_py_common.device_info.is_voq_chassis = mock.MagicMock(return_value=True)
+            if os.environ["UTILITIES_UNIT_TESTING_IS_PACKET_CHASSIS"] == "1":
+                sonic_py_common.device_info.is_voq_chassis = mock.MagicMock(return_value=False)
+                sonic_py_common.device_info.is_packet_chassis = mock.MagicMock(return_value=True)
+            else:
+                sonic_py_common.device_info.is_voq_chassis = mock.MagicMock(return_value=True)
             SonicV2Connector.delete_all_by_pattern = mock.MagicMock()
     if os.environ["UTILITIES_UNIT_TESTING_TOPOLOGY"] == "multi_asic":
         import mock_tables.mock_multi_asic

tests/portstat_db/on_sup_packet_chassis/chassis_state_db.json

@@ -0,0 +1,2 @@
+{
+}