TCP wait_for transmit question

[Anil Madhavapeddy <anil@xxxxxxxxxx>]

Haris just raised an interesting point on IRC.  He wants to limit the amount of 
data sent on TCP write, which is normally done via TCP.Pcb.write_wait_for 
<bytes>.

This function calls the User_buffer.TX, which clamps it to the TX transmit 
window, which we ideally want to keep full at all times.

Do we need another function to wait for space to be free in the TX.User_buffer 
(if it's greater than max_size), which will more closely match the UNIX 
write(2) semantics?  That is, write works until the transmit buffer is full, 
providing the TCP stack with more leeway to schedule on-the-wire packets.

-anil