Return an error if LinkLoss is disabled
Return an error if LinkLoss is disabled

Changes SetProperty method of the Proximity Monitor to verify if the
LinkLoss service is enabled before allowing to change the alert level.
Not available error is returned if LinkLoss service is disabled in the
Proximity configuration file.

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