HEADS-UP: Removal of FLIP support for xennet(4)/xvif(4)

[Jaromír Doleček <jaromir.dolecek%gmail.com@localhost>]

Hello,

I'd like to completely remove the support for old FLIP mode (page
transfer) from xennet(4)/xvif(4)

Main consideration is that actually FLIP mode is not actually used any
more by our oldest supported Xen 4.2, so right now it's just dead
code. The COPY performs better on MP systems, where the cost of page
table manipulations and cache flushes dwarfs any gains from avoiding
memory to memory copy.

I'm currently working on some optimisations for xennet(4), and keeping
the FLIP code paths makes the task really convoluted, especially since
I can't really even test it still works.

Unless there is some serious objection to the contrary, I'll remove
the FLIP/transfer related code from xennet(4) and xvif(4) in about 2
weeks from now.

Jaromir