net: thunderbolt: use eth_hw_addr_set()

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 go through appropriate helpers.

Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Link: https://lore.kernel.org/r/20211026175547.3198242-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>