tests: Bluetooth: df: Add tests for enable CTE req and sampling HCI cmd

Add unit tests for HCI commands:
- HCI_LE_Set_Connection_CTE_Receive_Parameters,
- HCI_LE_Connection_CTE_Request_Enable.
Tests validate current implementation of commands handling in HCI/ULL.
Handling of the HCI_LE_Connection_CTE_Request_Enable is not complete,
thus tests don't validate positive behavior the functions.

Signed-off-by: Piotr Pryga <piotr.pryga@nordicsemi.no>