simplify WiFi boot procedure to prepare for on-demand stack load

currently ```esp_wifi_init``` have to be called in ```app_main``` or
WiFi will fail to boot. When possible to boot later, code will be moved
into ```_esp_wifi_start``` to be executed when necessary

cores/esp32/main.cpp

@@ -8,15 +8,11 @@ extern "C" void initArduino();
 extern void loop();
 extern void setup();
 
-void startWiFi() __attribute__((weak));
-void startWiFi() {}
-
 void loopTask(void *pvParameters)
 {
     bool setup_done = false;
     for(;;) {
         if(!setup_done) {
-            startWiFi();
             setup();
             setup_done = true;
         }

libraries/WiFi/src/WiFiGeneric.cpp

@@ -40,14 +40,75 @@ extern "C" {
 #include "lwip/opt.h"
 #include "lwip/err.h"
 #include "lwip/dns.h"
+#include "esp_ipc.h"
 
 #include "esp32-hal-log.h"
+
+/**
+ * Boot and start WiFi
+ * This method get's called on boot if you use any of the WiFi methods.
+ * If you do not link to this library, WiFi will not be started.
+ * */
+static bool _esp_wifi_initalized = false;
+extern void initWiFi()
+{
+    wifi_init_config_t cfg = WIFI_INIT_CONFIG_DEFAULT();
+    tcpip_adapter_init();
+    esp_event_loop_init(&WiFiGenericClass::_eventCallback, NULL);
+    esp_wifi_init(&cfg);
+    esp_wifi_set_storage(WIFI_STORAGE_RAM);
+    _esp_wifi_initalized = true;
 }
 
+} //extern "C"
+
 #undef min
 #undef max
 #include <vector>
 
+static bool _esp_wifi_start()
+{
+    static bool started = false;
+    esp_err_t err;
+
+    if(!_esp_wifi_initalized){
+        initWiFi();
+        if(!_esp_wifi_initalized){
+            log_w("not initialized");
+            return false;
+        }
+    }
+    if(started){
+        return true;
+    }
+    started = true;
+    err = esp_wifi_start();
+    if (err != ESP_OK) {
+        log_e("%d", err);
+        return false;
+    }
+#if CONFIG_AUTOCONNECT_WIFI
+    wifi_mode_t mode = WIFI_MODE_NULL;
+    bool auto_connect = false;
+
+    err = esp_wifi_get_mode(&mode);
+    if (err != ESP_OK) {
+        log_e("esp_wifi_get_mode: %d", err);
+        return false;
+    }
+
+    err = esp_wifi_get_auto_connect(&auto_connect);
+    if ((mode == WIFI_MODE_STA || mode == WIFI_MODE_APSTA) && auto_connect) {
+        err = esp_wifi_connect();
+        if (err != ESP_OK) {
+            log_e("esp_wifi_connect: %d", err);
+            return false;
+        }
+    }
+#endif
+    return true;
+}
+
 // -----------------------------------------------------------------------------------------------------------------------
 // ------------------------------------------------- Generic WiFi function -----------------------------------------------
 // -----------------------------------------------------------------------------------------------------------------------
@@ -167,7 +228,11 @@ void WiFiGenericClass::persistent(bool persistent)
  */
 bool WiFiGenericClass::mode(wifi_mode_t m)
 {
-    if(getMode() == m) {
+    wifi_mode_t cm = getMode();
+    if(cm == WIFI_MODE_MAX){
+        return false;
+    }
+    if(cm == m) {
         return true;
     }
     return esp_wifi_set_mode(m) == ESP_OK;
@@ -180,6 +245,9 @@ bool WiFiGenericClass::mode(wifi_mode_t m)
 wifi_mode_t WiFiGenericClass::getMode()
 {
     uint8_t mode;
+    if(!_esp_wifi_start()){
+        return WIFI_MODE_MAX;
+    }
     esp_wifi_get_mode((wifi_mode_t*)&mode);
     return (wifi_mode_t)mode;
 }
@@ -275,48 +343,3 @@ void wifi_dns_found_callback(const char *name, const ip_addr_t *ipaddr, void *ca
     _dns_busy = false;
 }
 
-/**
- * Boot and start WiFi
- * This method get's called on boot if you use any of the WiFi methods.
- * If you do not link to this library, WiFi will not be started.
- * */
-#include "nvs_flash.h"
-
-extern "C" void initWiFi()
-{
-    wifi_init_config_t cfg = WIFI_INIT_CONFIG_DEFAULT();
-    nvs_flash_init();
-    tcpip_adapter_init();
-    esp_event_loop_init(WiFiGenericClass::_eventCallback, NULL);
-    esp_wifi_init(&cfg);
-}
-
-void startWiFi()
-{
-    esp_err_t err;
-
-    err = esp_wifi_start();
-    if (err != ESP_OK) {
-        log_e("esp_wifi_start: %d", err);
-        return;
-    }
-#if CONFIG_AUTOCONNECT_WIFI
-    wifi_mode_t mode = WIFI_MODE_NULL;
-    bool auto_connect = false;
-
-    err = esp_wifi_get_mode(&mode);
-    if (err != ESP_OK) {
-        log_e("esp_wifi_get_mode: %d", err);
-        return;
-    }
-
-    err = esp_wifi_get_auto_connect(&auto_connect);
-    if ((mode == WIFI_MODE_STA || mode == WIFI_MODE_APSTA) && auto_connect) {
-        err = esp_wifi_connect();
-        if (err != ESP_OK) {
-            log_e("esp_wifi_connect: %d", err);
-        }
-    }
-#endif
-}
-