wifi: mac80211_hwsim: track active STA links

Track the powersave bit on frames where we can look up
the STA by link addresses and set the links active or
inactive accordingly, and use this information to TX
only on links that are actually active in the peer.

Note that this doesn't implement powersave fully so
if no link is active things will not work right.

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