NetworkManager does not allow multiple VPN autoconnects

[Kaz Wolfe]

NetworkManager's Connection Editor does not support the ability to select multiple VPN connections to be established upon connection, as seen in https://i.stack.imgur.com/WJanI.png

However, this is very much supported according to the nm-settings page which allows multiple secondary connections (see https://developer.gnome.org/NetworkManager/unstable/nm-settings.html). This has been tested to work as well.

As such, the GUI should support the same ability as the command-line config. Perhaps replace the plain dropdown with a multi-select dropdown?

Affects version 1.2.6-0ubuntu0.16.04.2.