From: Shradha Shah <redacted>
Date: Fri, 29 May 2015 11:01:06 +0100

In the case where we have multiple functions (PFs and VFs), this
sysfs entry is useful to identify the physical port corresponding
to the function we are interested in.

Signed-off-by: Shradha Shah <redacted>

Please don't invent your own stuff for this, you are not the only driver
in the world that might want to export this kind of information.

Set netdev->dev_port properly and it'll already be exported for you
using portable, standard interfaces, that a user can use with any
device in the world, not just your's.