ble_adapter: Fix LE Secure Connections pairing

[mkarhumaa]

When pc-ble-driver-py was used on central side for initiating LE Secure Connections pairing against peripheral which does not support LE SC, pairing timed out because pc-ble-driver-py was waiting for event gap_evt_lesc_dhkey_request.

Fix is to expect BLEEvtID.gap_evt_lesc_dhkey_request only when both of the devices support LE Secure Connections.

[CLAassistant]

All committers have signed the CLA.

[jupe]

@jornbh could you review this as well. We would need this patch.

[jornbh]

Now, the tests have passed.