The ieee80211_sta_free_hw_features() function is now used outside
the MLME code, so better make sure it gets included in the build
to avoid leaking memory.
Get rid of wpa_supplicant_sta_rx() and add a new driver event that is
marked to be used only with driver_test.c. In addition, remove this
functionality from privsep wrapper. This is only use for client mode
MLME testing with driver_test.c.