MFC r338993:
When multiple threads are involved receiving completion events in LibUSB
make sure there is always a master polling thread, by setting the "ctx_handler"
field in the context. Else the reception of completion events can stop.
This happens if event threads are created and destroyed during runtime.

Found by: Ludovic Rousseau <ludovic.rousseau+freebsd@gmail.com>
PR: 231742
Sponsored by: Mellanox Technologies

MFC r338679:
Improve LibUSB debugging by simultaneously allowing both function
and transfer prints. Make sure the debug level comes from the
correct USB context.

Found by: Ludovic Rousseau <ludovic.rousseau+freebsd@gmail.com>
PR: 231264
Sponsored by: Mellanox Technologies

MFC r338616:
Fix issues about cancelling USB transfers in LibUSB when the USB device has
been detached. When a USB device has been detached the kernel file handle
stops responding to commands. USB applications which continue to run after
the USB device has been detached, depend on LibUSB generated events to tear
down its pending USB transfers. Add code to handle the needed cleanup when
processing the USB transfer(s) fails and prevent new USB transfer(s) from
being submitted.

Found by: Ludovic Rousseau <ludovic.rousseau+freebsd@gmail.com>
PR: 231076
Sponsored by: Mellanox Technologies

MFC r301956, r301957, r301964, r301966, r301968, r301969, r302080,
r302125 and r302171:

Added multiple new LibUSB v1.0 API functions.
Refer to the individual commits for more details.

MFC r260315:
Implement two new libusb API functions.

PR: usb/185454

MFC r260315:
Implement two new libusb API functions.

PR: usb/185454