Proper place and exact change to increase the tx power in ble_app_att_mtu_throughput example(nRF5_SDK_15.0.0)

Hardware used: 2 nRF52480 DK boards 

I am running nRF5_SDK_15.0.0_a53641a\examples\ble_central_and_peripheral\experimental\ble_app_att_mtu_throughput example, I want to increase the tx power of the both sender and receiver boards.

I am adding the below change to increase the tx power of the nRF52840 boards to run the att_mtu example. But tx power value is not changing.

I checked the tx power value by keeping the debug breakpoint in the adv_data.c file(ble_advdata_encode()). Please help me regarding the changes need to be added, so that i can increase tx power and test the att_mtu example by keeping the 2 boards in long range.

ble_advdata_encode(): // Here everytime it is showing tx power level to zero.

// Encode TX power level.
if (p_advdata->p_tx_power_level != NULL)
{
err_code = tx_power_level_encode(*p_advdata->p_tx_power_level,
p_encoded_data,
p_len,
max_size);
VERIFY_SUCCESS(err_code);
}

int main(void)
{
// Initialize.
log_init();
cli_init();
leds_init();
timer_init();
counter_init();
buttons_init();
power_management_init();
ble_stack_init();
gap_params_init();
+ sd_ble_gap_tx_power_set(BLE_GAP_TX_POWER_ROLE_CONN,m_conn_handle,8);
+ sd_ble_gap_tx_power_set(BLE_GAP_TX_POWER_ROLE_ADV,m_conn_handle,8);
gatt_init();
advertising_data_set();

---

}