The window scale option (http://tools.ietf.org/html/rfc1323) patch of lwIP
definitely works solely for the receive window, not for the send window.
Setting the send window size to the maximum of an 16bit value, 65535,
or multiple of it (x * 65536 - 1) results in the same performance.
Everything else decrease performance.
We will have to check this window scale patch before using higher values.
776a8d3f8c