unit/test-gatt: Add TP/GAR/CL/BV-07-C/512B test
unit/test-gatt: Add TP/GAR/CL/BV-07-C/512B test

Verify that a Generic Attribute Profile client can read a characteristic
descriptor by selected handle. The Characteristic Descriptor length is
unknown to the client and might be long with a value of 512 bytes.

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