[vlan][dhcp_relay] Clear dhcpv6 relay counter while deleting vlan (#2852)

What I did
Fix this issue: sonic-net/sonic-buildimage#15047
Show dhcp_relay ipv6 counter will display vlan which has been deleted.

How I did it
Remove related info in state_db while deleting a vlan

How to verify it
Add unit test
Build utilities and run cmd to verify

Signed-off-by: Yaqiang Zhu <[email protected]>

Author: yaqiangz

config/vlan.py

@@ -1,6 +1,7 @@
 import click
 import utilities_common.cli as clicommon
 import utilities_common.dhcp_relay_util as dhcp_relay_util
+from swsscommon.swsscommon import SonicV2Connector
 
 from time import sleep
 from .utils import log
@@ -64,6 +65,14 @@ def is_dhcpv6_relay_config_exist(db, vlan_name):
         return True
 
 
+def delete_state_db_entry(entry_name):
+    state_db = SonicV2Connector()
+    state_db.connect(state_db.STATE_DB)
+    exists = state_db.exists(state_db.STATE_DB, 'DHCPv6_COUNTER_TABLE|{}'.format(entry_name))
+    if exists:
+        state_db.delete(state_db.STATE_DB, 'DHCPv6_COUNTER_TABLE|{}'.format(entry_name))
+
+
 @vlan.command('del')
 @click.argument('vid', metavar='<vid>', required=True, type=int)
 @click.option('--no_restart_dhcp_relay', is_flag=True, type=click.BOOL, required=False, default=False,
@@ -106,6 +115,8 @@ def del_vlan(db, vid, no_restart_dhcp_relay):
     # set dhcpv4_relay table
     set_dhcp_relay_table('VLAN', db.cfgdb, vlan, None)
 
+    delete_state_db_entry(vlan)
+
     if not no_restart_dhcp_relay and is_dhcpv6_relay_config_exist(db, vlan):
         # set dhcpv6_relay table
         set_dhcp_relay_table(DHCP_RELAY_TABLE, db.cfgdb, vlan, None)

tests/vlan_test.py

@@ -391,10 +391,12 @@ def test_config_vlan_del_vlan(self, mock_restart_dhcp_relay_service):
             print(result.output)
             assert result.exit_code == 0
 
-        result = runner.invoke(config.config.commands["vlan"].commands["del"], ["1000"], obj=db)
-        print(result.exit_code)
-        print(result.output)
-        assert result.exit_code == 0
+        with mock.patch("config.vlan.delete_state_db_entry") as delete_state_db_entry:
+            result = runner.invoke(config.config.commands["vlan"].commands["del"], ["1000"], obj=db)
+            print(result.exit_code)
+            print(result.output)
+            assert result.exit_code == 0
+            delete_state_db_entry.assert_called_once_with("Vlan1000")
 
         # show output
         result = runner.invoke(show.cli.commands["vlan"].commands["brief"], [], obj=db)