LU-592 1.8 <-> 2.1 interop: missing LMV on client

LU-592 1.8 <-> 2.1 interop: missing LMV on client

When the cluster is upgraded from 1.8, client will not have LMV layer,
and the "ll_md_exp" is pointing to MDC directly, so the code which
assuming "ll_md_exp" as LMV need be revised:

- ll_dir_ioctl(LL_IOC_GETOBDCOUNT) should return 1 for MDC case;
- mdc_iocontrol() needs to handle the OBD_IOC_QUOTACTL as well when the
  "ll_md_exp" is MDC;

Signed-off-by: Niu Yawei <niu@whamcloud.com>
Change-Id: I3659a5f8076125c9b2012826521c44540e65a75e
Reviewed-on: http://review.whamcloud.com/1236
Tested-by: Hudson
Reviewed-by: Fan Yong <yong.fan@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>