gattrib: Fix protection of GAttrib while calling callbacks
gattrib: Fix protection of GAttrib while calling callbacks

The callbacks could result with the reference count dropping to 0 and
the object being freed. This patch fixes the issue by adding one extra
reference for the duration of the timeout function.

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