doc: netlink: Fix op pre and post fields in generated .rst

The generated .rst has pre and post headings without any values, e.g.
here:

https://docs.kernel.org/6.9/networking/netlink_spec/dpll.html#device-id-get

Emit keys and values in the generated .rst
Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20240528140652.9445-5-donald.hunter@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/net/ynl/ynl-gen-rst.py

@@ -156,7 +156,10 @@ def parse_do(do_dict: Dict[str, Any], level: int = 0) -> str:
     lines = []
     for key in do_dict.keys():
         lines.append(rst_paragraph(bold(key), level + 1))
+        if key in ['request', 'reply']:
             lines.append(parse_do_attributes(do_dict[key], level + 1) + "\n")
+        else:
+            lines.append(headroom(level + 2) + do_dict[key] + "\n")
 
     return "\n".join(lines)