Add support for CLAT using a BPF program
Summary
Implements a CLAT (part of a larger 464XLAT ipv6 transition mechanism) in NetworkManager
Purpose
See #1435. This MR adds a CLAT and autodetection of the pref64/pfx96/whatever prefix using the PREF64 router advertisement option. It does not add support for the special ipv4only.arpa domain (I would like some advice on how to do this for a future change)
Checklist
Please read https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/blob/main/CONTRIBUTING.md before opening the merge request. In particular, check that:
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the subject for all commits is concise and explicative -
the message for all commits explains the reason for the change -
the source is properly formatted -
any relevant documentation is up to date -
you have added unit tests if applicable -
the NEWS file is updated when the change deserves to be mentioned, for example for new features, behavior changes, API deprecations, etc.