Each NML3ConfigData should have a source set, and in fact most callers
would call nm_l3_config_data_set_source() right after creating the
instance.
Move the source parameter to the new() constructor function. Also remove
the setter, making the source of an instance immutable.
As every l3cfg instance generally has a clear purpose, the source should
always be known from the start and doesn't need to change.
We use the merge function to initialize the cloned instance.
Previously, merge did not always copy all properties, so the
cloned instance might not have been identical. Fix that.
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
