Use the new hostapd functionality (in LEDE) to detect 802.11r and 802.11w
more properly. Leave the old logic in place for Openwrt.
Adjust 802.11w default value from "0" to "" in order to avoid unnecessary
"option ieee80211w 0" lines in /etc/config/wireless
Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>