windows 7: nativewifi bearer plugin doesn't complete QNetworkConfigurationManager::updateConfigurations()

After calling updateConfigurations(), the updateCompleted() signal is never emitted.
Debugging shows the callback is received from the generic plugin but not the nativewifi plugin.

Test case: tst_qnetworkconfigurationmanager::allConfigurations

Test fails even if the timeout is increased to 3 minutes.
Test passes if wifi is switched off, or if run on a desktop PC with no wifi adaptor.

Note that the initial update during construction is successful.