Bluetooth: controller: complete DF TX params set in conn mode

HCI_LE_Set_Connection_CTE_Transmit_Parameters host command was
not completely implemented in controller. There were missign
storage of TX parameters in ll_conn instance.

The commit adds missing part of the command handling.

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