mac80211: support NL80211_EXT_FEATURE_CONTROL_PORT_OVER_NL80211_MAC_ADDRS

This is now a trivial patch, but for seeing the actual changes
I (Johannes) split it out from the original.

Signed-off-by: Markus Theil <markus.theil@tu-ilmenau.de>
Link: https://lore.kernel.org/r/20200115125522.3755-1-markus.theil@tu-ilmenau.de
[split into separate cfg80211/mac80211 patches]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>