LU-8778 osd: osd_index_declare_ea_delete() reserve more credits

LU-8778 osd: osd_index_declare_ea_delete() reserve more credits

when ".." direntry is being removed, OSD may need to update
local representative (agent inodes). reserve additional
credits for these updates.

Change-Id: I3689239ac9e7859fbb4a7c6edc87aa3d59a6be7e
Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-on: http://review.whamcloud.com/23486
Tested-by: Jenkins
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: wangdi <di.wang@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>