android/gatt: Make att_handler use g_attrib buffer
android/gatt: Make att_handler use g_attrib buffer

This makes use of g_attrib buffer for output and removes some unused
read_by_group_type function parameters.

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