staging/lustre/mdc: use cl_max_mds_md to pack getattr RPC

In some cases, cl_default_mds_easize might be zero, especially for
MDC connected to non-MDT0, then mdc might pack getattr RPC with
zero eadatasize.

If client is trying to access remote striped directory with
zero eadatasize, MDT will not return layout information of the
striped direcotry, which will be mis-regarded as non-striped
directory.

So we should use cl_max_mds_easize if cl_default_mds_easize is zero.

Signed-off-by: wang di <di.wang@intel.com>
Reviewed-on: http://review.whamcloud.com/9862
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-4847


Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>