LU-4976 osp: add doxygen comments for osp_object.c functions

LU-4976 osp: add doxygen comments for osp_object.c functions

Add introductory comment block for the osp_object.c file. And add
function comment blocks to all functions in the osp_object.c file.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: Id228c3612df3391f9307e39c6dcb30e60cf1665d
Reviewed-on: http://review.whamcloud.com/10799
Reviewed-by: Ned Bass <bass6@llnl.gov>
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Andreas Dilger <andreas.dilger@intel.com>