staging: usbip: prevent possible buffer overflow reading port records

To avoid buffer overflow while reading a corrupted or possibly
modified port file we validate the length of each part of the port
record to ensure it doesn't exceed the length of the destination
buffer.

https://bugzilla.kernel.org/show_bug.cgi?id=69931

Signed-off-by: Mark Asselstine <asselsm@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>