queue.h: Add QLIST_FIX_HEAD_PTR() If the head of a list has been moved to a different memory location, the le_prev link in the first list entry has to be fixed up. Provide a macro that implements this fixup. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com>