Merge branch 'dsa-set_addr-optional'

John Crispin says:

====================
net-next: dsa: set_addr should be optional

The Marvell driver is the only one that actually sets the switches HW
address. All other drivers have an empty stub. fix this by making the
callback optional.
====================

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