gfs2: Store qd_id in struct gfs2_quota_data as a struct kqid

- Change qd_id in struct gfs2_qutoa_data to struct kqid.
- Remove the now unnecessary QDF_USER bit field in qd_flags.
- Propopoage this change through the code generally making
  things simpler along the way.

Cc: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>