Add documentation for the phys_port_id sysfs attribute of a network
device.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
                "unknown", "notpresent", "down", "lowerlayerdown", "testing",
                "dormant", "up".
 
+What:          /sys/class/net/<iface>/phys_port_id
+Date:          July 2013
+KernelVersion: 3.12
+Contact:       netdev@vger.kernel.org
+Description:
+               Indicates the interface unique physical port identifier within
+               the NIC, as a string.
+
 What:          /sys/class/net/<iface>/speed
 Date:          October 2009
 KernelVersion: 2.6.33