staging: lustre: lmv: change handling of lmv striping information

The lmv_[un]pack_md function are used to calculate the
size of the data used to represent the LMV striping data.
The original code was straight forward in its calculate
with lmv_get_easize since only one type of data format
could exist. We want to be able to support different
version of this data in the future so this patch moves
to generating the size of the data using the stripe count
and which LMV_MAGIC_* version.

Signed-off-by: wang di <di.wang@intel.com>
Reviewed-on: http://review.whamcloud.com/7043
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3531


Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>