Modified the cc2420 driver to enable the radio test
mode to emit unmodulated carriers (tones).
A carrier can be enabled using the normal radio driver
API:
NETSTACK_CONF_RADIO.set_value(
RADIO_PARAM_POWER_MODE,
RADIO_POWER_MODE_CARRIER_ON);
Once enabled, the carrier can be disabled like this:
NETSTACK_CONF_RADIO.set_value(
RADIO_PARAM_POWER_MODE,
RADIO_POWER_MODE_CARRIER_OFF);
