Merge branch 'bpf-bpftool-cleanups'

Quentin Monnet says:

====================
This series contains several minor fixes for bpftool source and
documentation.

The first patches focus on documentation: addition of an option in the page
for "bpftool prog", clean up and update of the same page, and addition of
an example of prog array map manipulation in "bpftool map" page.

The last two fix warnings susceptible to appear when libbfd is not present
(patch 4), or with additional warning flags passed to the compiler (last
patch).
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>