core/gatt: Send not/ind for D-Bus characteristics
core/gatt: Send not/ind for D-Bus characteristics

This patch adds support for sending out notification/indication packets
for external characteristics whenever a PropertiesChanged signal is
received for the "Value" property of an external characteristic that has
either the 'notify' or the 'indicate' property.

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