make drone's WPA configuration persistent

wpa.sh

#!/bin/sh

# Append
# /home/default/wpa.sh &
# to /bin/wifi_setup.sh

# The desired IP address for the drone
ADDRESS="192.168.x.y"

# WPA credentials for the new network
ESSID="some_ssid"
PASSWORD="password"

wpa_passphrase $ESSID $PASSWORD > /etc/wpa_supplicant.conf

# shorten this when everything is confirmed working
sleep 100

{ ifconfig ath0 $ADDRESS; iwconfig ath0 essid '$ESSID' && wpa_supplicant -B -Dwext -iath0 -c/etc/wpa_supplicant.conf; } &