Fix: lower down the message logging level for unmanaged DHCP request

Change-Id: I4f2e9031685c20eed9e6a3208056e7953a835e2c
diff --git a/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackSwitchingDhcpHandler.java b/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackSwitchingDhcpHandler.java
index adc6bad..788ecee 100644
--- a/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackSwitchingDhcpHandler.java
+++ b/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackSwitchingDhcpHandler.java
@@ -252,7 +252,7 @@
                     .findAny().orElse(null);
 
             if (port == null) {
-                log.warn("Failed to retrieve openstack port information for MAC {}", clientMac);
+                log.debug("Ignore DHCP request, since it comes from unmanaged openstack VM {}", clientMac);
                 return;
             }