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>
xen-unstable changeset: 24950:9ef985f5e6a5
xen-unstable date: Thu Mar 01 16:37:18 2012 +0000

     1.1 --- a/xen/common/grant_table.c	Wed Mar 07 08:35:58 2012 +0000
     1.2 +++ b/xen/common/grant_table.c	Wed Mar 07 08:39:21 2012 +0000
     1.3 @@ -574,6 +574,8 @@ static void
     1.4              act->start = 0;
     1.5              act->length = PAGE_SIZE;
     1.6              act->is_sub_page = 0;
     1.7 +            act->trans_dom = rd->domain_id;
     1.8 +            act->trans_gref = op->ref;
     1.9          }
    1.10      }
    1.11