adb/fastboot: Support SuperSpeed USB devices

When enumerating USB 3.0 devices, a 6-byte SuperSpeed companion
descriptor follows each standard descriptor. The ADB and Fastboot
Linux clients currently fail to interpret these additional
descriptors and simply bail. Fix this by skipping over them.

Change-Id: I254dad8ed81e8de74a4fac36e8ce54b5da9715fe