tcp_rmem[1] has been changed to 131072, we should update the documentation
to reflect this.

Fixes: a337531b ("tcp: up initial rmem to 128KB and SYN rwin to around 64KB")
Signed-off-by: NEric Dumazet <edumazet@google.com>
Reported-by: NZhibin Liu <zhibinliu@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>