Clear value after each wifi network

src/freedombone-wifi

         if [ ${#WIFI_PASSPHRASE} -gt 1 ]; then
             echo "$WIFI_PASSPHRASE" >> $WIFI_NETWORKS_FILE
         fi
+
+        # clear values
+        WIFI_SSID=
+        WIFI_PASSPHRASE=
+
         wifi_ctr=$((wifi_ctr + 1))
     done
 }