This patch introduces userspace-only USB passthrough using libusb. It
supports configuring passthrough via a (passthru.vid.pid) tuple.
Currently, only vendor and product ID-based selection is implemented;
selecting specific ugen devices (to differentiate between identical
devices) would require changes to libusb.
All USB transfer types—control, bulk, interrupt, and isochronous—are
supported. Hotplugging is also handled, allowing devices to be unplugged
when guest startup and replugged afterward without issue.
Sponsored by: The FreeBSD Foundation