nfs41: Client indicates presence of NFSv4.1 callback channel.

Set the SESSION4_BACK_CHAN flag to indicate the client supports a backchannel.
Signed-off-by: Ricardo Labiaga <ricardo.labiaga@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>

fs/nfs/nfs4proc.c

@@ -4598,7 +4598,7 @@ static int _nfs4_proc_create_session(struct nfs_client *clp)
 	int status;
 
 	nfs4_init_channel_attrs(&args);
-	args.flags = (SESSION4_PERSIST);
+	args.flags = (SESSION4_PERSIST | SESSION4_BACK_CHAN);
 
 	status = rpc_call_sync(session->clp->cl_rpcclient, &msg, 0);