tests: Bluetooth: df: Missing conf for max num of CTE in per adv chain

Implementation of ll_df_set_cl_cte_tx_params was updated to verify
if the number of requested CTE in a periodic advertising chain is less
or equal to maximum supported value that is provided by CONFIG_BT_CTLR-
_DF_PER_ADV_CTE_NUM_MAX Kconfig option. In the past the value was
verified against maximum value allowed by BT Core Spec Vol 4, Part E,
section 7.8.80. Check against BT Core spec provided value could lead to
memory overwrite.

The unit tests start to fail because default value of the CONFIG_BT_-
CTLR_DF_PER_ADV_CTE_NUM_MAX is 1, hence is shall be changed in unit test
configuration file.

The commit adds missing configuration.

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