net: dsa: retain a per-port device_node pointer

We will later use the per-port device_node pointer to fetch a bunch of
port-specific properties.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc include/net/dsa.h
Simple merge

diff --cc net/dsa/dsa.c
Simple merge

diff --cc net/dsa/slave.c
Simple merge