Add udesc_dump(1.3.6), it showes USB descriptors and is useful for
helping debug USB device(driver).
maho@ is gathering reports from users to compile a FreeBSD-ready
USB device list. udesc_dump is exceptionally useful for that
purpose and should be made handily available.
Approved by: portmgr (knu)
Reviewed by: Jigoku <gehenna@jp.FreeBSD.org>