Previously, NMUtilsShareRules basically was tracking a list of command
line arguments, and during apply(), it would spawn the (iptables)
processes.
But in practice, this list was always pre-determined by a few
parameters, the interface name and the subnet. Instead of keeping the
list of arguments, only keep those few parameters. And generate the list
of arguments only for the short time when we need them.
The difference is that we will want to support nftables too. Later,
we can just generate a different list of commands, but there is no
need to keep this list around.
In core, NMPlatform is (also) a singleton instance. As we will move platform code
to libnm-platform, this singleton part makes no sense there. Move the code
to NetworkManagerUtils.c.
Currently "src/" mostly contains the source code of the daemon.
I say mostly, because that is not true, there are also the device,
settings, wwan, ppp plugins, the initrd generator, the pppd and dhcp
helper, and probably more.
Also we have source code under libnm-core/, libnm/, clients/, and
shared/ directories. That is all confusing.
We should have one "src" directory, that contains subdirectories. Those
subdirectories should contain individual parts (libraries or
applications), that possibly have dependencies on other subdirectories.
There should be a flat hierarchy of directories under src/, which
contains individual modules.
As the name "src/" is already taken, that prevents any sensible
restructuring of the code.
As a first step, move "src/" to "src/core/". This gives space to
reorganize the code better by moving individual components into "src/".
For inspiration, look at systemd's "src/" directory.
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/743
