staging: fsl-dpaa2: ethsw: Handle SWITCHDEV_PORT_ATTR_SET

Following patches will change the way we communicate setting a port's
attribute and use a blocking notifier to perform those tasks.

Prepare ethsw to support receiving notifier events targeting
SWITCHDEV_PORT_ATTR_SET and simply translate that into the existing
swdev_port_attr_set() call.

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