selftests/bpf: add BPF object fixup step to veristat

selftests/bpf: add BPF object fixup step to veristat

Add a step to attempt to "fix up" BPF object file to make it possible to
successfully load it. E.g., set non-zero size for BPF maps that expect
max_entries set, but BPF object file itself doesn't have declarative
max_entries values specified.

Another issue was with automatic map pinning. Pinning has no effect on
BPF verification process itself but can interfere when validating
multiple related programs and object files, so veristat disabled all the
pinning explicitly.

In the future more such fix up heuristics could be added to accommodate
common patterns encountered in practice.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20221005161450.1064469-3-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>