Completing low-level radio driver definition.

Completing the definition of 'receive_802154_packet_callback_t' type (i.e.: callback function type for incoming 802.15.4 packets), part of the API defined in PR #925.
1) Add an initialization function to the radio driver API.
2) The physical radio transceiver drivers always have quality indicators available with incoming packets, the corresponding callback type is thus extended to handle them.