msgp codegen requires structs to be pointers

[skaldesh]

The msgp codegen tool produces code like this:

// EncodeMsg implements msgp.Encodable
func (z *UpdateBatchOpClassifyAndPauseSettingsArg) EncodeMsg(en *msgp.Writer) (err error) {
	// map header, size 1
	// write "AnomalySeverities"
	fmt.Println("EncodeMsg from generated code")
	err = en.Append(0x81, 0xb1, 0x41, 0x6e, 0x6f, 0x6d, 0x61, 0x6c, 0x79, 0x53, 0x65, 0x76, 0x65, 0x72, 0x69, 0x74, 0x69, 0x65, 0x73)
	if err != nil {
		return
	}
	err = en.WriteArrayHeader(uint32(len(z.AnomalySeverities)))
	if err != nil {
		err = msgp.WrapError(err, "AnomalySeverities")
		return
	}
	for za0001 := range z.AnomalySeverities {
		err = en.WriteUint8(z.AnomalySeverities[za0001])
		if err != nil {
			err = msgp.WrapError(err, "AnomalySeverities", za0001)
			return
		}
	}
	return
}

But our orbit tool generates this:

func (v1 *client) UpdateBatchOpClassifyAndPauseSettings(ctx context.Context, arg UpdateBatchOpClassifyAndPauseSettingsArg) (err error) {
	if v1.callTimeout > 0 {
		var cancel context.CancelFunc
		ctx, cancel = context.WithTimeout(ctx, v1.callTimeout)
		defer cancel()
	}
	err = v1.Call(ctx, CallIDUpdateBatchOpClassifyAndPauseSettings, arg, nil)
	if err != nil {
		return
	}
	return
}

Note the missing Pointer of arg
This causes the generated msgp code to not being used, producing in the worst case incompatible encodings for the service side (or the other way around).