docs: netdev: refine the clean-up patch examples

docs: netdev: refine the clean-up patch examples

We discourage sending trivial patches to clean up checkpatch warnings.
There are other tools which lead to patches of similarly low value
like some coccicheck warnings. The warnings are useful for new code
but fixing them in the existing code base is a waste of review time.

Broaden the example given in the doc a little bit.

Link: https://patch.msgid.link/20250815165242.124240-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>