Given that root hub port peers are already established, external hub peer
ports can be determined by traversing the device topology:
1/ ascend to the parent hub and find the upstream port_dev
2/ walk ->peer to find the peer port
3/ descend to the peer hub via ->child
4/ find the port with the matching port id
Note that this assumes the port labeling scheme required by the
specification [1].
[1]: usb3 3.1 section 10.3.3
Acked-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>