of: net: add a helper for loading netdev->dev_addr

[ Upstream commit d466effe ]

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.

There are roughly 40 places where netdev->dev_addr is passed
as the destination to a of_get_mac_address() call. Add a helper
which takes a dev pointer instead, so it can call an appropriate
helper.

Note that of_get_mac_address() already assumes the address is
6 bytes long (ETH_ALEN) so use eth_hw_addr_set().

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: 1d6d537d ("net: ethernet: mtk_eth_soc: handle probe deferral")
Signed-off-by: Sasha Levin <sashal@kernel.org>