Bluetooth: Controller: Rename lll_df_conf_cte_tx_disable()

Rename lll_df_conf_cte_tx_disable() to lll_df_cte_tx_disable()
so that it can be used as a common function between connection
and connectionless implementations.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>