Introduce two more layers between device and endpoint:

device -> active config -> claimed interface -> endpoints.
Device can have at most one active config. A config can have
multiple claimed interfaces, each with a specific alt setting.
An interface with an alt setting defines a list of endpoints.

usb/descriptor.go

@@ -15,6 +15,8 @@
 
 package usb
 
+import "fmt"
+
 // Descriptor is a representation of a USB device descriptor.
 type Descriptor struct {
 	// Bus information
@@ -37,3 +39,8 @@ type Descriptor struct {
 	// Configuration information
 	Configs []ConfigInfo
 }
+
+// String represents a human readable representation of the device in the descriptor.
+func (d *Descriptor) String() string {
+	return fmt.Sprintf("vid=%s,pid=%s,bus=%d,addr=%d", d.Vendor, d.Product, d.Bus, d.Address)
+}