Modify EndpointInfo to provide meaningful data rather than raw USB

descriptor values. E.g. for the user, the distinction between
MaxIsoPkt and MaxPktSize is irrelevant, only the calculated max packet
size matters.

usb/device.go

@@ -92,7 +92,7 @@ func (d *Device) Close() error {
 	return nil
 }
 
-func (d *Device) OpenEndpoint(cfgNum, ifNum, setNum, epNum uint8) (*Endpoint, error) {
+func (d *Device) OpenEndpoint(epNum, cfgNum, ifNum, setNum uint8) (*Endpoint, error) {
 	var cfg *ConfigInfo
 	for _, c := range d.Configs {
 		if c.Config == cfgNum {
@@ -132,7 +132,7 @@ func (d *Device) OpenEndpoint(cfgNum, ifNum, setNum, epNum uint8) (*Endpoint, er
 
 	var ep *EndpointInfo
 	for _, e := range ifs.Endpoints {
-		if e.Address == epNum {
+		if e.Number == epNum {
 			debug.Printf("found ep %02x in %#v\n", epNum, *ifs)
 			ep = &e
 		}