LU-10531 gss: fix GSS support for DNE

LU-10531 gss: fix GSS support for DNE

Part of the patch https://review.whamcloud.com/24236 was
inadvertently reverted by patch https://review.whamcloud.com/27823.
So re-apply missing part to have full DNE support in GSS code.

This patch is necessary because with DNE, an OSP can be used on MDT
for connections to other MDTs. So to determine exactly every
connection's purpose, use client_obd's cl_sp_to in
import_to_gss_svc().

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I029dbfc52eeabb2c6f0f6d2c972ceea1879405e7
Reviewed-on: https://review.whamcloud.com/30984
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>