LU-8471 obdclass: restore EXPORT_SYMBOL for lu_ref* functions

LU-8471 obdclass: restore EXPORT_SYMBOL for lu_ref* functions

LU-5829 removed a lot of EXPORT_SYMBOL, including for the lu_ref_*
functions. As these functions are only compiled in when the
--enable-lu_ref is passed to configure, the breakage was missed. This
patch restores the missing EXPORT_SYMBOLS that were present, except
for lu_ref_print and lu_ref_is_marker which are only used in the
obdclass module.

Test-Parameters: trivial
Signed-off-by: Frank Zago <fzago@cray.com>
Change-Id: I16e6065b75c568a18386c0f0a746484fdad38d6e
Reviewed-on: http://review.whamcloud.com/21640
Reviewed-by: Andrew Perepechko <andrew.perepechko@seagate.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>