Merge branch 'bpf-bpftool-dbg-output'

Quentin Monnet says:

====================
This series adds an option to bpftool to make it print additional
information via libbpf and the kernel verifier when attempting to load
programs.

A new API function is added to libbpf in order to pass the log_level
from bpftool with the bpf_object__* part of the API.

Options for a finer control over the log levels to use for libbpf and
the verifier could be added in the future, if desired.

v3:
- Fix and clarify commit logs.

v2:
- Do not add distinct options for libbpf and verifier logs, just keep the
  one that sets all log levels to their maximum. Rename the option.
- Do not offer a way to pick desired log levels. The choice is "use the
  option to print all logs" or "stick with the defaults".
- Do not export BPF_LOG_* flags to user header.
- Update all man pages (most bpftool operations use libbpf and may print
  libbpf logs). Verifier logs are only used when attempting to load
  programs for now, so bpftool-prog.rst and bpftool.rst remain the only
  pages updated in that regard.

Previous discussion available at:

https://lore.kernel.org/bpf/20190523105426.3938-1-quentin.monnet@netronome.com/
https://lore.kernel.org/bpf/20190429095227.9745-1-quentin.monnet@netronome.com/
====================

Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>