tools: usb: p9_fwd: add usb gadget packet forwarder script

This patch is adding an small python tool to forward 9pfs requests
from the USB gadget to an existing 9pfs TCP server. Since currently all
9pfs servers lack support for the usb transport this tool is an useful
helper to get started.

Refer the Documentation section "USBG Example" in
Documentation/filesystems/9p.rst on how to use it.

Signed-off-by: Jan Luebbe <jlu@pengutronix.de>
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Tested-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
Link: https://lore.kernel.org/r/20240116-ml-topic-u9p-v12-3-9a27de5160e0@pengutronix.de


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>