See FreeBSD Setup for /boot/loader.conf, also /etc/start_if.rum0 (start_if.ifN):
wlans_rum0="wlan0" create_args_wlan0="wlandev rum0 wlanmode hostap" ifconfig_wlan0="inet 10.50.90.1 netmask 255.255.255.0 ssid unwiredbsd mode 11g"
/etc/rc.conf
hostapd_enable="YES"
/etc/hostapd.conf
interface=wlan0 debug=1 ctrl_interface=/var/run/hostapd ctrl_interface_group=wheel ssid=unwiredbsd wpa=1 wpa_passphrase=0x1deadbeef9 wpa_key_mgmt=WPA-PSK wpa_pairwise=CCMP TKIP
sudo /etc/rc.d/hostapd forcestart