tested on RTL8168d/8111d model using 'super_netperf 40' with TCP/UDP_STREAM.

Output of
while true; do
    for n in inflight limit; do
          echo -n $n\ ; cat $n;
    done;
    sleep 1;
done

during netperf run, 100mbit peer:

inflight 0
limit 3028
inflight 6056
limit 4542

[ trimmed output for brevity, no limit/inflight changes during
  test steady-state ]

limit 4542
inflight 3028
limit 6122
inflight 0
limit 6122
[ changed cable to 1gbit peer, restart netperf ]
inflight 37850
limit 36336
inflight 33308
limit 31794
inflight 33308
limit 31794
inflight 27252
limit 25738
[ again, no changes during test ]
inflight 27252
limit 25738
inflight 0
limit 28766
[ change cable to 100mbit peer, restart netperf ]
limit 28766
inflight 27370
limit 28766
inflight 4542
limit 5990
inflight 6056
limit 4542
[ .. ]
inflight 6056
limit 4542
inflight 0

[end of test]

Cc: Francois Romieu <romieu@fr.zoreil.com>
Cc: Hayes Wang <hayeswang@realtek.com>
Signed-off-by: NFlorian Westphal <fw@strlen.de>
Acked-by: NEric Dumazet <edumazet@google.com>
Acked-by: NTom Herbert <therbert@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>