Using param structure in VIF interface

["Durrant, Paul" <xadimgnik@xxxxxxxxx>]

Just to let you know that I am working on this...

It's more of a can of worms than I thought... Now that I have split up 
the patches I realise that, to use a params structure, we need that to 
be versioned along with the interface. Also when XENNET is using a 
down-rev version, which could theoretically be behind the latest version 
in XENVIF, we are going to need a chain of callback functions to 
translate each version of the params structure to/from the previous 
version until we get to the one that XENNET actually deals with.
I have something partially done, but it's going to take another day or so.

  Paul