LU-4791 lod: subtract xattr overhead when calculate max EA size.

LU-4791 lod: subtract xattr overhead when calculate max EA size.

1. It needs to subtract the xattr overhead when calculate the max
EA size, otherwise, it might get oversize stripe_count, which cause
ENOSPC error in the following xattr_set.
2. Release stripe information, if xattr set fails.

Lustre-change: http://review.whamcloud.com/9835
Lustre-commit: a11c69ad81ca8071b9d97d5032539dd7b36873ee

Change-Id: I4a4fe0681f2cd9dd6f242a03c75326acde02ae05
Signed-off-by: wang di <di.wang@intel.com>
Reviewed-on: http://review.whamcloud.com/10020
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>