mac80211: Simplify Extended Key ID API

1) Drop IEEE80211_HW_EXT_KEY_ID_NATIVE and let drivers directly set
   the NL80211_EXT_FEATURE_EXT_KEY_ID flag.

2) Drop IEEE80211_HW_NO_AMPDU_KEYBORDER_SUPPORT and simply assume all
   drivers are unable to handle A-MPDU key borders.

The new Extended Key ID API now requires all mac80211 drivers to set
NL80211_EXT_FEATURE_EXT_KEY_ID when they implement set_key() and can
handle Extended Key ID. For drivers not providing set_key() mac80211
itself enables Extended Key ID support, using the internal SW crypto
services.

Signed-off-by: Alexander Wetzel <alexander@wetzel-home.de>
Link: https://lore.kernel.org/r/20190629195015.19680-2-alexander@wetzel-home.de
Signed-off-by: Johannes Berg <johannes.berg@intel.com>