$ find * -type f |xargs perl contrib/scripts/spdx.pl
  $ git rm contrib/scripts/spdx.pl

- don't let no_auto_default_from_file() do any preprocessing of
  the lines that it reads. It merely splits the lines at '\n'
  and utf8safe-unescapes them.
  This was previously duplicated also by NMConfigData's property
  setter. We don't need to do it twice.

- sort the lines. This makes the entire handling O(n*ln(n)) instead
  of O(n^2). Also, sorting effectively normalizes the content, and
  it's desirable to have one true representation of what we write.

For devices that have no real MAC address (virtual devices) it makes no
sense to store the MAC address to "no-auto-default.state" file. Also,
because we later would not match the MAC address during
nm_match_spec_device().

Instead, extend the format and add a "interface-name:=$IFACE" match-spec.

Maybe we generally should prefer the interface-name over the MAC
address. Anyway, for now, just extend the previously non-working case.

The define is better, because then we can grep for all the occurances
where they are used. The plain text like "mac:" is not at all unique in
our source-tree.

We no longer add these. If you use Emacs, configure it yourself.

Also, due to our "smart-tab" usage the editor anyway does a subpar
job handling our tabs. However, on the upside every user can choose
whatever tab-width he/she prefers. If "smart-tabs" are used properly
(like we do), every tab-width will work.

No manual changes, just ran commands:

    F=($(git grep -l -e '-\*-'))
    sed '1 { /\/\* *-\*-  *[mM]ode.*\*\/$/d }'     -i "${F[@]}"
    sed '1,4 { /^\(#\|--\|dnl\) *-\*- [mM]ode/d }' -i "${F[@]}"

Check remaining lines with:

    git grep -e '-\*-'

The ultimate purpose of this is to cleanup our files and eventually use
SPDX license identifiers. For that, first get rid of the boilerplate lines.

"nm-macros-interal.h" already includes <errno.h> and <string.h>.
No need to include it everywhere else too.

Each time when enabling/disabling "systemd-resolved" in combination with another
plugin (which is unchanged), another pair of signal handlers was
connected. That's wrong.

Fixes: d4eb4cb45f41b1751cacf71da558bf8f0988f383