shared/gatt: Fix memory leak in discovery_op_unref
shared/gatt: Fix memory leak in discovery_op_unref

Free services list in discovery_op_unref. If discovery has been
interrupted, services from discovery_op were not pushed to
gatt_client service list, and it caused memory leak.

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