LU-8880 gss: fix GSS support for DNE

LU-8880 gss: fix GSS support for DNE

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() and gss_svc_upcall_install_rvs_ctx().

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I84934010102bdf760d07796866272b359bf0465e
Reviewed-on: https://review.whamcloud.com/24236
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: wangdi <di.wang@intel.com>