[th/fix-lgpl-license-violations] Fix wrongly using GPL code in libnm

libnm is supposed to be LGPL-2.1+ licensed. Currently, the library wrongly includes some files which are GPL-2.0+. This needs to be fixed.

Such license violations happened because of mistakes. Also, it was an easy mistake to make. That is because having GPL and LGPL code in the same repository is error prone and a limitation. One day in the future, we may want attempt to relicense all code under LGPL. For now, just fix things that are clearly wrong.

Also note that for a while already every contribution to NetworkManager MUST be LGPL-2.1+ licensed already ([1]).

Most of the code here are just header files (so it's not clear how copyrightable those even are). Anyway, I won't bother arguing that agreement of actual or perceived copyright holders isn't necessary for this fix. Instead, I will request all potential copyright holders to agree to this (or at least, explicitly disagree, so I can determine which contributions are actually affected and sort those out). This means, please, everybody relevant agree/disagree to this change (I will reach out to people separately). Even if it's not clear whether you are actually relevant for this, please still better agree/disagree explicitly.

In fact, I won't even bother to get approvement for this branch only. Instead, I would wish that copyright holders agree (or disagree) to this and future changes right away. This is tracked and explained in RELICENSE.md file.

Next steps: track agreement/disagreement for all potentially affected copyright holders in RELICENSE.md file.

Fixes: #270 (closed)