Proxy fixes and logging clarity improvements

[akvadrako]

While working on the raw_gadget backend I was mostly using the proxy device. However there were several issues with it that prevented it from working. This fixes those.

It also fixes a few things that were not correct according to the libusb docs, like forwarding SET_INTERFACE to the real device - it should be handled specially.

There are also some suggestions for logging to make it more clear and have a level where it's less verbose.

[xairy]

It would be great to split these changes into separate commits with separate descriptions of what each change does.

But I'll leave reviewing this to the Facedancer developers.