Document GNetwork Monitors
https://developer.gnome.org/gio/stable/GNetworkMonitor.html says there are two ways to detect the online status: NetworkManager and Netlink. With
GIO_USE_NETWORK_MONITOR the network monitor can be set. If I read the source code correctly, for
GIO_USE_NETWORK_MONITOR valid values are base, networkmanager, portal and netlink.
Please describe, if GIO_USE_NETWORK_MONITOR is not set (how can I found out which manager is used), which manager is choosen by glib and how do portal and base work.