https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/789

Like with "libnm-core/", split "libnm/" into different directories for
the public headers, for the implementation and for the helper "aux"
library.

"libnm-core/" is rather complicated. It provides a static library that
is linked into libnm.so and NetworkManager. It also contains public
headers (like "nm-setting.h") which are part of public libnm API.

Then we have helper libraries ("libnm-core/nm-libnm-core-*/") which
only rely on public API of libnm-core, but are themself static
libraries that can be used by anybody who uses libnm-core. And
"libnm-core/nm-libnm-core-intern" is used by libnm-core itself.

Move "libnm-core/" to "src/". But also split it in different
directories so that they have a clearer purpose.

The goal is to have a flat directory hierarchy. The "src/libnm-core*/"
directories correspond to the different modules (static libraries and set
of headers that we have). We have different kinds of such modules because
of how we combine various code together. The directory layout now reflects
this.

And example script for getting and setting OVS external-ids.

Since currently there is no nmcli support for these properties yet,
the script becomes more interesting.

This "example" is rather long, and it showcases less the usage of
libnm (which is rather trivial, with respect to configuring
NMSettingOvsExternalIDs). Instead, it aims to provide a useful
command line tool for debugging. Hence, it's mostly concerned with
an elaborate command line syntax and useful print output.

This is useful for manually testing Update2() D-Bus API.

This is useful for manually testing AddConnection2() D-Bus API.

Use the script to test how GObject introspection with libnm's WireGuard
support works.

Also, since support for WireGuard peers is not yet implemented in nmcli
(or other clients), this script is rather useful.

It's not an example and not actually used.

https://github.com/NetworkManager/NetworkManager/pull/141