Only write wifi interface if parameters are given

src/freedombone-utils-wifi

 }
 
 function create_networks_interactive {
+    remove_config_param "WIFI_INTERFACE"
     update_wifi_adaptors
     if [ ! $IFACE ]; then
         # Don't try to configure wifi if there are no adaptors
-        remove_config_param "WIFI_INTERFACE"
         return
     fi
-    write_config_param "WIFI_INTERFACE" "$WIFI_INTERFACE"
 
     if [ -f $WIFI_NETWORKS_FILE ]; then
         rm $WIFI_NETWORKS_FILE
         if [ ${#WIFI_SSID} -gt 1 ]; then
             if [ ${#WIFI_TYPE} -gt 1 ]; then
                 if [[ "${WIFI_TYPE}" == $'none' || "${WIFI_TYPE}" == $'open' ]]; then
+                    write_config_param "WIFI_INTERFACE" "$WIFI_INTERFACE"
                     return
                 else
                     if [ ${#WIFI_PASSPHRASE} -gt 1 ]; then
+                        write_config_param "WIFI_INTERFACE" "$WIFI_INTERFACE"
                         return
                     fi
                 fi