Merge branch 'Prepare veristat for packaging'

Andrii Nakryiko says:

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This patch set relicenses veristat.c to dual GPL-2.0/BSD-2 license and
prepares it to be mirrored to Github at libbpf/veristat repo.

Few small issues in the source code are fixed, found during Github sync
preparetion.

v2->v3:
  - fix few warnings about uninitialized variable uses;
v1->v2:
  - drop linux/compiler.h and define own ARRAY_SIZE macro;
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Signed-off-by: Alexei Starovoitov <ast@kernel.org>