LU-1914 ldlm: add doxygen comments

LU-1914 ldlm: add doxygen comments

Update original patch from bugzilla b=20943 written by Oleg Drokin for
master.  Extensively document functions, data structures and
subsystems in the ldlm module.  Make various improvements to language
and formatting of existing comments.  Complete conversion of major
struct definitions to tab indentation.

Signed-off-by: Ned Bass <bass6@llnl.gov>
Oracle-bug-id: b=20943
Change-Id: I10086a1be943b2b473f90129bc2d6abab31d9bd7
Reviewed-on: http://review.whamcloud.com/3985
Tested-by: Hudson
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>