staging: lustre: ptlrpc: ret -ECONNREFUSED if not context found in req

Return -ECONNREFUSED instead of -ENOMEM in sptlrpc_req_get_ctx()
if no context is found in req. It is more graceful.

Signed-off-by: Sebastien Buisson <sebastien.buisson@bull.net>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-6356
Reviewed-on: http://review.whamcloud.com/14043


Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Andrew Perepechko <andrew.perepechko@seagate.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>