[RFC SKBUFF]: Keep track of writable header len of headerless clones

[David Miller]

From: Patrick McHardy <kaber at trash.net>
Date: Sun, 24 Jun 2007 14:53:36 +0200

> - sendmsg eth0, no NAT:		sys     0m2.508s
> - sendmsg eth0, NAT:		sys     0m2.539s
> - sendmsg eth0, NAT + patch:	sys     0m2.445s	(no change)

This is probably because we're touching all the data anyways
and if the resident set size is small enough (as a gigabit
or 100MB ethernet TCP stream window would be) then it all fits
mostly in the L2 caches of the cpu.

Oh yeah and I like your patch Patrick :-)