bluetooth: use dev_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.

Reviewed-by: Marcel Holtmann <marcel@holtmann.org>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>