rps: document flow limit in scaling.txt
rps: document flow limit in scaling.txt

Explain the mechanism and API of the recently merged
rps flow limit patch.

Signed-off-by: Willem de Bruijn <1ee125182537a91f90180f97fc3b3cb011bdf78a@google.com>
Signed-off-by: David S. Miller <fe08d3c717adf2ae63592e4c9aec6e3e404d8e3e@davemloft.net>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs