Grant table: fix a bug when grant copying a previous grant mapped page.

Grant table: fix a bug when grant copying a previous grant mapped page.

In grant table version 2, when we create a non-transitive mapping from
DomU to Dom0, we need to set active entry's trans_domain and
trans_ref.  Otherwise when we grant copy from this previous mapped
ref, preemption count will get messed up.

See changeset 22994:299ed79acecf for more information.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Committed-by: Keir Fraser <keir@xen.org>