docs: netdev: try to guide people on dealing with silence

There has been more than a few threads which went idle before
the merge window and now people came back to them and started
asking about next steps.

We currently tell people to be patient and not to repost too
often. Our "not too often", however, is still a few orders of
magnitude faster than other subsystems. Or so I feel after
hearing people talk about review rates at LPC.

Clarify in the doc that if the discussion went idle for a week
on netdev, 95% of the time there's no point waiting longer.

Link: https://lore.kernel.org/r/20231120200109.620392-1-kuba@kernel.org


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