ethernet: constify references to netdev->dev_addr in drivers

This big patch sprinkles const on local variables and
function arguments which may refer to netdev->dev_addr.

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.

Some of the changes here are not strictly required - const
is sometimes cast off but pointer is not used for writing.
It seems like it's still better to add the const in case
the code changes later or relevant -W flags get enabled
for the build.

No functional changes.

Link: https://lore.kernel.org/r/20211014142432.449314-1-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>