gdbus: Use object manager only if callback functions are set
gdbus: Use object manager only if callback functions are set

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