LU-6376 osp: add RPC lock during RPC send

LU-6376 osp: add RPC lock during RPC send

Add RPC lock in osp_remote_sync(), so only one modified
UPDATE RPC is allowed each time as other normal MDC client.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: I6c766625adc355d5c8827bffb78a1820efc46fd6
Reviewed-on: http://review.whamcloud.com/14098
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>