nm_settings_get_best_connections() has only one caller: to create
the hidden-SSID list.

Instead of having a highly specialised function (that accepts 3 ways for
filtering -- one of them broken, has one hard-coded way of sorting, and
a @max_requested argument), add a more generic nm_settings_get_connections_clone()
function.

Also invert nm_settings_sort_connections(). The two callers want
to sort descending, not ascending.