ethernet: tulip: remove direct netdev->dev_addr writes

Consify the casts of netdev->dev_addr.

Convert pointless to eth_hw_addr_set() where possible.

Use local buffers in a number of places.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>