Network: added notify settings updated method.

* And call it from the DNS client -- this is the only add-on that does
  not trigger a configuration or settings update, so we have to notify
  the changes manually.

headers/os/add-ons/network_settings/NetworkSettingsAddOn.h

@@ -27,10 +27,6 @@ enum BNetworkSettingsType {
 	B_NETWORK_SETTINGS_TYPE_OTHER = 'othr'
 };
 
-enum {
-	kMsgSettingsItemUpdated = 'SIup'
-};
-
 class BNetworkProfile;
 class BNetworkSettings;
 
@@ -70,6 +66,8 @@ public:
 	virtual void				SettingsUpdated(uint32 type);
 	virtual void				ConfigurationUpdated(const BMessage& message);
 
+	virtual	void				NotifySettingsUpdated();
+
 private:
 			const BNetworkProfile*
 								fProfile;