Update xenvif to #8 ca17715a7e8c323eee505db4dba99d6fe0f72cb1

Signed-off-by: Ben Chalmers <Ben.Chalmers@citrix.com>
Merge pull request #12 from benchalmers/xenvif8

Update xenvif to #8 ca17715a7e8c323eee505db4dba99d6fe0f72cb1

Accepted-By: Ben Chalmers <ben.chalmers@citrix.com>