wifi: add SoftAPModeProbeRequestReceived event handler (#2917)

- add probe request event handler (#2910)
- update WiFi events handling example to use new handler

Pro tip: replace blinking LED with ‘analogWrite’ and connect the pin to
a loudspeaker (or use a servo to hit a bell). Get notified when someone
with a smartphone wanders around your country house.

libraries/ESP8266WiFi/src/ESP8266WiFiGeneric.h

@@ -61,6 +61,7 @@ class ESP8266WiFiGenericClass {
         WiFiEventHandler onStationModeDHCPTimeout(std::function<void(void)>);
         WiFiEventHandler onSoftAPModeStationConnected(std::function<void(const WiFiEventSoftAPModeStationConnected&)>);
         WiFiEventHandler onSoftAPModeStationDisconnected(std::function<void(const WiFiEventSoftAPModeStationDisconnected&)>);
+        WiFiEventHandler onSoftAPModeProbeRequestReceived(std::function<void(const WiFiEventSoftAPModeProbeRequestReceived&)>);
         // WiFiEventHandler onWiFiModeChange(std::function<void(const WiFiEventModeChange&)>);
 
         int32_t channel(void);