staging: usbip: userspace: add support for viewing imported devices

As of Matt Mooney's major refactoring in 2011, usbip port
option was left out. Add support for this option in
a manner similar to the old implementation.

Sample output:

Imported USB devices
====================
Port 00: <Port in Use> at Full Speed(12Mbps)
       unknown vendor : unknown product (1687:6211)
       2-1 -> usbip://192.168.122.152:3240/1-1
           -> remote bus/dev 001/002

Signed-off-by: Valentina Manea <valentina.manea.m@gmail.com>
Reviewed-by: Ilija Hadzic <ihadzic@research.bell-labs.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>