[dhcp_relay][telemetry] Update events test for dhcp6relay bind issue (#…

…16216)

What is the motivation for this PR?
There are global unique ipv6 address and link local ipv6 address configured in Vlan, not need to flush all of them to trigger fail to bind issue.

How did you do it?
Only delete GUA in Vlan

How did you verify/test it?
Run test

tests/telemetry/events/dhcp-relay_events.py

@@ -56,21 +56,29 @@ def trigger_dhcp_relay_bind_failure(duthost):
 
     vlan = dhcp_test_info["vlan"]
     dhcp6_relay_process = dhcp_test_info["dhcp6relay_process"]
-    ipv6_ip = dhcp_test_info["ipv6_address"]
+    ipv6_global_unique_ip = dhcp_test_info["ipv6_address"]
 
     try:
         # Flush ipv6 address from vlan
-        duthost.shell("ip -6 address flush dev {}".format(vlan))
+        duthost.shell("ip -6 address del {} dev {}".format(ipv6_global_unique_ip, vlan))
 
         # Restart dhcrelay process
         duthost.shell("docker exec dhcp_relay supervisorctl restart {}".format(dhcp6_relay_process))
+        # Wait dhcp6relay to hit bind failure, dhcp6relay would try 6 times with interval 5s, hence wait 35s to hit
+        # bind failure
+        time.sleep(35)
 
     finally:
         # Add back ipv6 address to vlan
-        duthost.shell("ip address add {} dev {}".format(ipv6_ip, vlan))
-
-        # Restart dhcrelay process
-        duthost.shell("docker exec dhcp_relay supervisorctl restart {}".format(dhcp6_relay_process))
+        duthost.shell("ip address add {} dev {}".format(ipv6_global_unique_ip, vlan))
+
+        # After bind failure test, dhcp6relay would exit because fail to bind. It's critical process of dhcp_relay,
+        # hence maybe in that time dhcp_relay container has crashed, we need to restart whole dhcp_relay service to
+        # recover
+        duthost.shell("systemctl reset-failed dhcp_relay")
+        duthost.restart_service("dhcp_relay")
+        py_assert(wait_until(100, 10, 0, duthost.is_service_fully_started_per_asic_or_host, "dhcp_relay"),
+                  "dhcp_relay not started.")
 
 
 def send_dhcp_discover_packets(duthost, ptfadapter, packets_to_send=5, interval=1):