Set scan_duplicate in BLE scan params

[buxtronix]

This value is uninitialised and as such can be a random (and invalid) value. It's needs to be set per the espressif documentation here:

https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/bluetooth/esp_gap_ble.html#_CPPv4N21esp_ble_scan_params_t14scan_duplicateE

This PR sets it to DUPLICATE_DISABLE. Chosen as this is needed to ensure all scan data is populated in the scan callback, per this comment in the IDF:

https://github.com/espressif/esp-idf/blob/master/components/bt/host/bluedroid/stack/btm/btm_ble_gap.c#L3591

"//if scan duplicate is enabled, the adv packet without scan response is allowed to report to higher layer"

We don't want it to report to the higher layer (ie BLEScan.cpp) unless it has the active scan response.

Seems to resolve #3770 #3677 and possibly others.

[chegewara]

Strange, i never needed that to get duplicates in v1.0.4, but maybe in master it is set to true in idf.

[h2zero]

From my testing in NimBLE this will you get a lot of spam packets (and callbacks) if disabled (0x0), better make sure wantDuplicates in BLEScan::setAdvertisedDeviceCallbacks is false.

Although it may work different in bluedroid, but I doubt it, the same command is sent to the controller.

You should consider adding a method to BLEScan in this PR to allow the app to control this.
Here is what I have in the NimBLE library:

void NimBLEScan::setDuplicateFilter(bool active) {
    m_scan_params.filter_duplicates = active;
} // setDuplicateFilter

[buxtronix]

setAdvertisedDeviceCallbacks already contains a parameter wantDuplicates, which is whether to filter dupes in BLEScan.