What does the RSSI values mean in emberEnergyScanResultHandler() & emberGetLastHopRssi()?

In emberGetLastHopRssi() the RSSI value is of data type int8s, which is the RSSI energy level in dBm.

In emberEnergyScanResultHandler() the RSSI value is of data type int8u. This is the raw RSSI value straight from the radio, which is offset by -154 from the actual dBm value measured.  So take your unsigned 8-bit result, subtract 154 from that, and that is the RSSI energy level in dBm for that channel.