server: update default value of setting 'expose.dns.externally' to 'false' (apache#8776)

Author: weizhouapache

server/src/main/java/com/cloud/network/router/VirtualNetworkApplianceManager.java

@@ -72,7 +72,7 @@ public interface VirtualNetworkApplianceManager extends Manager, VirtualNetworkA
             "If true, router minimum required version is checked before sending command", false);
     static final ConfigKey<Boolean> UseExternalDnsServers = new ConfigKey<Boolean>(Boolean.class, "use.external.dns", "Advanced", "false",
             "Bypass internal dns, use external dns1 and dns2", true, ConfigKey.Scope.Zone, null);
-    static final ConfigKey<Boolean> ExposeDnsAndBootpServer = new ConfigKey<Boolean>(Boolean.class, "expose.dns.externally", "Advanced", "true",
+    static final ConfigKey<Boolean> ExposeDnsAndBootpServer = new ConfigKey<Boolean>(Boolean.class, "expose.dns.externally", "Advanced", "false",
             "open dns, dhcp and bootp on the public interface", true, ConfigKey.Scope.Zone, null);
 
     static final ConfigKey<String> VirtualRouterServiceOffering = new ConfigKey<String>(String.class, VirtualRouterServiceOfferingCK, "Advanced", "",