drv/bluetooth_btstack: use static random address

This changes the bluetooth driver to give the device a new random
address each time the bluetooth chip resets.

Issue: pybricks/support#600

lib/pbio/drv/bluetooth/bluetooth_btstack.c

@@ -440,8 +440,20 @@ void pbdrv_bluetooth_init(void) {
     nordic_spp_service_server_init(nordic_spp_packet_handler);
 }
 
+static void handle_static_addr_random(void* arg) {
+    uint8_t *static_addr = arg;
+    // First two msb must be set to indicate static random address.
+    static_addr[0] |= 0xC0;
+    gap_random_address_set(static_addr);
+}
+
 void pbdrv_bluetooth_power_on(bool on) {
     hci_power_control(on ? HCI_POWER_ON : HCI_POWER_OFF);
+
+    // generate a new static/random address each time we reset the Bluetooth chip
+    static btstack_crypto_random_t static_addr_random;
+    static uint8_t static_addr[6];
+    btstack_crypto_random_generate(&static_addr_random, static_addr, sizeof(static_addr), handle_static_addr_random, static_addr);
 }
 
 bool pbdrv_bluetooth_is_ready(void) {