Add API to set advertising scheme on disconnected

[XuGuohui]

Problem

Currently when device acting as BLE peripheral is disconnected from peer device, it will re-start advertising automatically. In some use cases, user may wants to stop advertising on disconnected, unless otherwise user manually calls BLE.advertise() to start advertising.

Solution

Add wiring API to set advertising scheme for which after disconnected from peer deivce.

Example App

#include "application.h"

SYSTEM_MODE(MANUAL);

SerialLogHandler logHandler(LOG_LEVEL_ALL);

system_tick_t disconTime = 0;
bool restartAdv = false;

/* executes once at startup */
void setup() {
    // BLE.setAdvertisingScheme(BleAdvertisingScheme::RESTART_ADV_ON_DISCONNECTED);
    // BLE.setAdvertisingScheme(BleAdvertisingScheme::STOP_ADV_ON_DISCONNECTED);
    BLE.setAdvertisingScheme(BleAdvertisingScheme::STOP_ADV_ON_DISCONNECTED_ONCE);
    BLE.advertise();
    BLE.onDisconnected([&](const BlePeerDevice& peer) {
        disconTime = millis();
        restartAdv = true;
    });
}

/* executes continuously after setup() runs */
void loop() {
    if (restartAdv && (millis() - disconTime > 15000)) {
        restartAdv = false;
        if (!BLE.advertising()) {
            Log.info("Restarting advertising");
            BLE.advertise();
        }
    }
}

References

https://community.particle.io/t/ble-disconnect-works-but-then-reconnects/68469

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Completeness

• [x] User is totes amazing for contributing!
• [x] Contributor has signed CLA (Info here)
• [x] Problem and Solution clearly stated
• [ ] Run unit/integration/application tests on device
• [ ] Added documentation
• [ ] Added to CHANGELOG.md after merging (add links to docs and issues)