netdevice: demote the type of some dev_addr_set() helpers

__dev_addr_set() and dev_addr_mod() and pretty low level,
let the arguments be void, there's no chance for confusion
in callers converted to use them. Keep u8 in dev_addr_set()
because some of the callers are converted from a loop
and we want to make sure assignments are not from an array
of a different type.

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