Even Gentoo disables this plugin since before 0.9.8 release
of NetworkManager. Time to say goodbye.
If somebody happens to show up to maintain it, we may resurrect it
later.
If "$distro_plugins=ifnet" was set, configure.ac would use that
to autodetect --with-hostname-persist=gentoo. Replace that autodetect
part by checking for /etc/gentoo-release file.
Since meson 0.44 there is a new option type called `array`, which
allows to use an array with different values in those options.
These fits the needs of different options that are used to pass
binary paths, which have multiple paths as an alternate locations.
meson's version has been bumped to 0.44 and different options have
been changed to `array` type options.
https://mail.gnome.org/archives/networkmanager-list/2017-December/msg00062.html
There are three headers `nm-secret-agent-old.h`,
`nm-vpn-plugin-old.h`, and `nm-vpn-service-plugin.h`, which are
named as no introspection headers. However, these files also
join to the rest headers to generate introspection data.
This patch merges those no introspection headers with the public
headers.
