MITM_BOND supposedly doesn't have the problem mentioned in #266

(and it is good / more secure anyways - the old code was just
based on the example docs)

src/esp32/BluetoothUtil.cpp

@@ -309,7 +309,7 @@ BLEServer *initBLE(StartBluetoothPinScreenCallback startBtPinScreen, StopBluetoo
 
     // FIXME - really should be ESP_LE_AUTH_REQ_SC_BOND but it seems there is a bug right now causing that bonding info to be lost
     // occasionally?
-    pSecurity->setAuthenticationMode(ESP_LE_AUTH_REQ_SC_BOND);
+    pSecurity->setAuthenticationMode(ESP_LE_AUTH_REQ_SC_MITM_BOND);
 
     pSecurity->setInitEncryptionKey(ESP_BLE_ENC_KEY_MASK | ESP_BLE_ID_KEY_MASK);