Bluetooth: Controller: df: Fix wrong PHY type check in CTE req enable

CTE request may not be enabled when actual PHY does not support
transmission of constant tone extension. In case a connection is
asymetric, receive PHY is required to support transmission of CTE.
Receive PHY will be used by a device to get PDU with CTE.

In ll_df_set_conn_cte_req_enable was checking TX PHY type.
It should check RX PHY type.

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