Disable arp_evict_nocarrier for vlan host intf (#2590)

What I did
Cherry-pick back #2469 into 202205.

Why I did it
It is reverted in 202205: #2518 because of the flakiness of test_vlan.py

How I verified it
This depends on the following PRs:
#2504
#2541

cfgmgr/vlanmgr.cpp

@@ -134,6 +134,11 @@ bool VlanMgr::addHostVlan(int vlan_id)
     std::string res;
     EXEC_WITH_ERROR_THROW(cmds, res);
 
+    res.clear();
+    const std::string echo_cmd = std::string("")
+      + ECHO_CMD + " 0 > /proc/sys/net/ipv4/conf/" + VLAN_PREFIX + std::to_string(vlan_id) + "/arp_evict_nocarrier";
+    swss::exec(echo_cmd, res);
+
     return true;
 }
 

tests/test_vlan.py

@@ -490,6 +490,47 @@ def proxy_arp_disabled():
         self.dvs_vlan.remove_vlan_interface(vlan)
         self.dvs_vlan.remove_vlan(vlan)
 
+    def test_VlanMemberLinkDown(self, dvs):
+
+        # TODO: add_ip_address has a dependency on cdb within dvs,
+        # so we still need to setup the db. This should be refactored.
+        dvs.setup_db()
+
+        vlan = "1000"
+        vlan_ip = "192.168.0.1/21"
+        interface = "Ethernet0"
+        vlan_interface = "Vlan%s" % vlan
+        server_ip = "192.168.0.100"
+        neighbor_table = "NEIGH_TABLE:" + vlan_interface
+        vlan_intf_sysctl_param_path = "/proc/sys/net/ipv4/conf/%s/arp_evict_nocarrier" % vlan_interface
+
+        self.dvs_vlan.create_vlan(vlan)
+        vlan_oid = self.dvs_vlan.get_and_verify_vlan_ids(1)[0]
+        self.dvs_vlan.verify_vlan(vlan_oid, vlan)
+        self.dvs_vlan.create_vlan_member(vlan, interface)
+        self.dvs_vlan.verify_vlan_member(vlan_oid, interface)
+        dvs.set_interface_status(interface, "up")
+        dvs.add_ip_address(vlan_interface, vlan_ip)
+        dvs.runcmd("ip neigh replace %s lladdr 11:22:33:44:55:66 dev %s nud stale" % (server_ip, vlan_interface))
+
+        self.dvs_vlan.app_db.wait_for_matching_keys(neighbor_table, [server_ip])
+
+        # NOTE: arp_evict_nocarrier is available for kernel >= v5.16 and current
+        # docker-sonic-vs is based on kernel v5.4.0, so test only if this sysctl
+        # param is present
+        rc, res = dvs.runcmd("cat %s" % vlan_intf_sysctl_param_path)
+        if rc == 0:
+            assert res.strip() == "0"
+            dvs.set_interface_status(interface, "down")
+            self.dvs_vlan.app_db.wait_for_matching_keys(neighbor_table, [server_ip])
+
+        dvs.runcmd("ip neigh flush all")
+        dvs.remove_ip_address(vlan_interface, vlan_ip)
+        self.dvs_vlan.remove_vlan_member(vlan, interface)
+        self.dvs_vlan.get_and_verify_vlan_member_ids(0)
+        self.dvs_vlan.remove_vlan(vlan)
+        self.dvs_vlan.get_and_verify_vlan_ids(0)
+
 # Add Dummy always-pass test at end as workaroud
 # for issue when Flaky fail on final test it invokes module tear-down before retrying
 def test_nonflaky_dummy():