Zero-copy in the network stack

[IanSeyler]

http://en.wikipedia.org/wiki/Zero-copy

This is partially implemented.

b_net_tx forwards the memory location of the packet directly to the network driver and the hardware handles it. No time is spent by the CPU to copy anything.

b_net_rx does one copy (from the OS packet buffer to the requested memory address) via a nasty rep movsb so that will need to be adjusted in the network drivers.

On startup a default OS buffer location will be configured. Via a system call an application will be allowed to modify this to suit its own location.