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.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: Ibe46b8cbc161f151eae4eb14878af4406fc78d41
Reviewed-on: http://review.whamcloud.com/9835
Tested-by: Jenkins
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>