ethernet: replace netdev->dev_addr 16bit writes

Commit 406f42fa ("net-next: When a bond have a massive amount
of VLANs...") introduced a rbtree for faster Ethernet address look
up. To maintain netdev->dev_addr in this tree we need to make all
the writes to it got through appropriate helpers.

This patch takes care of drivers which cast netdev->dev_addr to
a 16bit type, often with an explicit byte order.

Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>