libusb: make hotplug callback handle an int

[bapt]

Summary

Change libusb_hotplug_callback_handle from a pointer to an int,
matching the sourceforge's libusb API.
Handle backward compatibility.

[bapt]

this one in particular I would love to get a review, this is the first time I plan with symbol version compatibility

[kib]

lib/libusb/libusb10_hotplug.c

531

Why not list the default symbols in Symbol.map?

538

This cannot work, you cannot export two different objects under same name+version. The point of versioning is to provide different versions.