ll: Initialize connection events counter to 0xFFFF so that the 1st CE sets it to 0
ll: add ll_pdu_data struct for Data packets
ll: central role - timers handling when going from Initiating to Connection state
ll: in ll_on_radio_rx(), rename rcvd_pdu by rcvd_adv_pdu to allow data PDUs as well
ll: in CONNECTION_MASTER state, start connection events by sending Empty PDUs
ll: in connection state, handle supervision timeout
ll: in CONNECTION_MASTER state, 1st draft for packet reception