Fixed WebSocket connection hang issue after listener reconfigure.

Because the configuration values were read from the listener's configuration,
an established WebSocket connection was unable to work properly (i. e. stuck)
if the listener was removed.  The correct source of configuration values is the
request config joint.

This is related to issue #581 on GitHub.

docs/changes.xml

@@ -37,6 +37,13 @@ fixed building with glibc 2.34, notably Fedora 35.
 </para>
 </change>
 
+<change type="bugfix">
+<para>
+established WebSocket connections could stop reading frames from the client
+after the corresponding listener had been reconfigured.
+</para>
+</change>
+
 </changes>