core: Fix GATT security level for non-paired devices
core: Fix GATT security level for non-paired devices

If we're not paired we shouldn't use medium security (which requires
pairing).

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