Merge branch 'libbpf: deprecate xdp_cpumap, xdp_devmap and classifier sec definitions'

Lorenzo Bianconi says:

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Deprecate xdp_cpumap, xdp_devmap and classifier sec definitions.
Update cpumap/devmap samples and kselftests.

Changes since v2:
- update warning log
- split libbpf and samples/kselftests changes
- deprecate classifier sec definition

Changes since v1:
- refer to Libbpf-1.0-migration-guide in the warning rised by libbpf
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Signed-off-by: Andrii Nakryiko <andrii@kernel.org>