staging: lustre: obdclass: add LCT_SERVER_SESSION for server session

Add LCT_SERVER_SESSION for server session, and separate the
server session flag from LCT_SESSION, so to avoid allocating
session info for client stack for each server request, if
client and server are on the same node.

Signed-off-by: Wang Di <di.wang@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3806
Reviewed-on: http://review.whamcloud.com/7412


Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>