Demand Attach: Volumes and vnodes are different

Demand Attach: Volumes and vnodes are different

fssync-debug attempts to copy sizeof(Volume) bytes into an object
defined as a Vnode, a sure fire way to make things go boom.

gcc on Snow Leopard picks this up as a buffer overflow, and warns about
it. Fix the problem by only copying sizeof(Vnode) bytes.

Change-Id: Iadcda0b465f9a9f310dcbe4d3862ea479e052674
Reviewed-on: http://gerrit.openafs.org/1834
Reviewed-by: Tom Keiser <tkeiser@sinenomine.net>
Reviewed-by: Alistair Ferguson <alistair.ferguson@mac.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>