doc: Clarify the value 127 for RSSI means unavailable
doc: Clarify the value 127 for RSSI means unavailable

pkarasev3/bluez,silent-snowman/bluez,pstglia/external-bluetooth-bluez,ComputeCycles/bluez,mapfau/bluez,mapfau/bluez,silent-snowman/bluez,silent-snowman/bluez,mapfau/bluez,pkarasev3/bluez,ComputeCycles/bluez,pkarasev3/bluez,silent-snowman/bluez,mapfau/bluez,ComputeCycles/bluez,pstglia/external-bluetooth-bluez,pstglia/external-bluetooth-bluez,pstglia/external-bluetooth-bluez,pkarasev3/bluez,ComputeCycles/bluez