usbip: prevent vhci_hcd driver from leaking a socket pointer address
When a client has a USB device attached over IP, the vhci_hcd driver is
locally leaking a socket pointer address via the
/sys/devices/platform/vhci_hcd/status file (world-readable) and in debug
output when "usbip --debug port" is run.
Fix it to not leak. The socket pointer address is not used at the moment
and it was made visible as a convenient way to find IP address from socket
pointer address by looking up /proc/net/{tcp,tcp6}.
As this opens a security hole, the fix replaces socket pointer address with
sockfd.