to save the resources and keep handler chain small if the feature is not used.
+add a warning message on settingsack_p page to restart on first activation
<td>Specifies if the proxy should send the X-Forwarded-For http header.</td>
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<tdcolspan="3"><inputtype="submit"class="btn btn-primary btn-sm"name="httpNetworking"value="Submit"/><em>Changes will take effect immediately.</em></td>
response.sendError(HttpServletResponse.SC_FORBIDDEN,"proxy use not allowed (see System Administration -> Advanced Settings -> Proxy Access Settings -> Transparent Proxy; switched off).");