Actually stop BLE scan in StopScan() on nrf528xx

[zopieux]

Tested on a nrf52840 board.

Without this patch, calling

Scan()
(sleep)
StopScan()
err := Scan()

returns an error on the second Scan() because the previous scan wasn't actually stopped, since the native call is missing.

With this patch, the above succeeds and the scan starts returning results, as usual.

I'm really not sure why there was a TODO rather than this simple function call. The TODO doesn't provide a rationale.

[deadprogram]

I'm really not sure why there was a TODO rather than this simple function call. The TODO doesn't provide a rationale.

Nor am I, but glad to have the correct implementation. Tested on one of my nrf52840 boards and does appear to work as expected and does not cause any unexpected side effects.

Thanks for the PR @zopieux now merging.