Bluetooth: host: direction: Remove compilation warning

Remove compilation warning caused by currently not used
hci_df_set_conn_cte_tx_param function.
Code is sorrounded by #ifdef CONFIG_BT_CTLR_DF_CONN_CTE_RSP.
The CONFIG_BT_CTLR_DF_CONN_CTE_RSP is changed to be disabled
by default (until complete implementation of the feature is
provided).

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