docs: networking: mention that RSS table should be 4x the queue count

docs: networking: mention that RSS table should be 4x the queue count

Spell out the recommendation that the RSS table should be
4x the queue count to avoid traffic imbalance. Include minor
rephrasing and removal of the explicit 128 entry example
since a 128 entry table is inadequate on modern machines.

Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260131225454.1225151-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>