Bluetooth: hci: Fix wrong CTE request interval type

Request interval is a number of connection events that
is used to periodically run CTE request control procedure.
BT 5.3 Core Specification defines it as 2 octets long.
It had wrong type uint8_t. Changed to correct one uint16_t.

The commit also changes type of cte_rsp_en field of lll_df_conn_tx_cfg
to state that it is a boolean flag.

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