mac80211_hwsim: notify wmediumd of used MAC addresses

Currently, wmediumd requires each used MAC address to be configured
as a station in the virtual air, but that doesn't make sense as any
station could have multiple MAC addresses, and even have randomized
ones in scanning, etc.

Add some code here to tell wmediumd of used MAC addresses, binding
them to the hardware address. Combined with a wmediumd patch that
makes it track the addresses this allows configuring just the radio
address (42:00:00:00:nn:00 unless the radio was manually created)
in wmediumd as a station, and all addresses that the station uses
are added/removed dynamically.

Tested with random scan, which without this and the corresponding
wmediumd change doesn't get anything through as the sender doesn't
exist as far as wmediumd is concerned (it's random).

Link: https://lore.kernel.org/r/20200323162358.b397b1a1acef.Ice0536e34e5d96c51f97c374ea8af9551347c7e8@changeid


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