tools/net/ynl-gen-rst: Remove extra indentation from generated docs

The output from ynl-gen-rst.py has extra indentation that causes extra
<blockquote> elements to be generated in the HTML output.

Reduce the indentation so that sphinx doesn't generate unnecessary
<blockquote> elements.

Reviewed-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20231215093720.18774-14-donald.hunter@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>