usbip: tools: add options and examples in man page related to device mode

usbip: tools: add options and examples in man page related to device mode

The commit f5742a2750fb ("usbip: tools: Start using VUDC backend in
usbip tools") implemented device mode for user space tools, however the
corresponding options are not documented in man page.

This commit documents the options and provides examples on device mode.
Also the command `usbip port` is documented.

Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Hongren Zheng <i@zenithal.me>
Link: https://lore.kernel.org/r/YFrdyKKx1nx8bktm@Sun
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>