NetworkAccessManager broken on macOS without bearermanagement

We encountered a bug in 5.14. If bearermanagement is disabled for Qt on macOS (-no-feature-bearermanagement) the QNetworkAccessManager cannot send requests, producing the error "Network access is disabled.".

The bug occurs because the NetworkStatusMonitor, which was introduced in 5.14 (https://codereview.qt-project.org/c/qt/qtbase/+/255898/38), does not check for disabled bearermanagement. The NetworkStatusMonitor is always enabled and cannot be disabled using other means, as the check for an environment variable has been removed (https://github.com/qt/qtbase/commit/8ac77123e287b13063a68ba2d48e0cc5cb24616d). When manually patching QNetworkStatusMonitor::isEnabled() in qtbase/src/network/kernel/qnetconmonitor_darwin.mm to always return false instead of true, the NetworkAccessManager can process requests again.

This behavior can be tested with the "qtbase/examples/download" example and any web ressource.