fixes hard fault when calling smart config with wifi off

[technobly]

In reference to this issue: https://github.com/spark/firmware/issues/310

Simply calling WiFi.on() after WiFi.disconnect() with Start_Smart_Config() ensures that calling WiFi.listen() (which effectively calls: Start_Smart_Config() ) always runs without failing (Hard Fault SOS) under the following test set:

Starting with the following 3 system modes:
SYSTEM_MODE(AUTOMATIC); // default behavior when no system mode is explicitly set
SYSTEM_MODE(MANUAL);
SYSTEM_MODE(SEMI_AUTOMATIC);

After calling:
Spark.connect();
Spark.disconnect();
WiFi.connect();
WiFi.disconnect();
WiFi.on();
WiFi.off();

We finally call:
WiFi.listen();

TEST APP

#include "application.h"

/* uncomment one of the following at a time */
//SYSTEM_MODE(AUTOMATIC); // default behavior when no system mode is explicitly set
//SYSTEM_MODE(MANUAL);
//SYSTEM_MODE(SEMI_AUTOMATIC);

void setup() {
  Serial.begin(9600);
}

void loop() {
  if (Serial.available()) {
    int c = Serial.read();
    switch (c) {
      case 'C': Spark.connect(); break;
      case 'c': Spark.disconnect(); break;
      case 'W': WiFi.connect(); break;
      case 'w': WiFi.disconnect(); break;
      case 'O': WiFi.on(); break;
      case 'o': WiFi.off(); break;
      case 'L': WiFi.listen(); break;
    }
  }
}