cfg80211: prepare for const netdev->dev_addr

netdev->dev_addr will be const soon.
All callers of wdev_address() can take const already.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20211019162816.1384077-2-kuba@kernel.org


Signed-off-by: Johannes Berg <johannes.berg@intel.com>