CA-115915: Network backend is not a VIF thing.

Note that this requires a xenopsd with with appropriate
changes in. (use CA-ticket to find the commit)

Signed-off-by: Jon Ludlam <jonathan.ludlam@eu.citrix.com>
Merge pull request #1500 from jonludlam/CA-115915

CA-115915: Network backend is not a VIF thing.