docs: netdev: rephrase the 'Under review' question

The semantics of "Under review" have shifted. Reword the question
about it a bit and focus it on the response time.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>