veristat: add -d debug mode option to see debug libbpf log

Add -d option to allow requesting libbpf debug logs from veristat.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230327185202.1929145-3-andrii@kernel.org


Signed-off-by: Alexei Starovoitov <ast@kernel.org>