ath6kl: use eth_hw_addr_set()

ath6kl: use eth_hw_addr_set()

Commit 406f42fa0d3c ("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.

Do the special encoding on the stack, then copy the address.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20211018235021.1279697-5-kuba@kernel.org