bpftool: Fix indent in option lists in the documentation

Mixed indentation levels in the lists of options in bpftool's
documentation produces some unexpected results. For the "bpftool" man
page, it prints a warning:

    $ make -C bpftool.8
      GEN     bpftool.8
    <stdin>:26: (ERROR/3) Unexpected indentation.

For other pages, there is no warning, but it results in a line break
appearing in the option lists in the generated man pages.

RST paragraphs should have a uniform indentation level. Let's fix it.

Fixes: c07ba629 ("tools: bpftool: Update and synchronise option list in doc and help msg")
Fixes: 8cc8c635

 ("tools: bpftool: Document and add bash completion for -L, -B options")
Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211110114632.24537-5-quentin@isovalent.com