hostapd: fix short_preamble option

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39027 3c298f89-4303-0410-b956-a3cf2f4a3e73
mac80211: add missing set_default to fix stray "radio0: sh: bad number" messages

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39028 3c298f89-4303-0410-b956-a3cf2f4a3e73