att: Fix sending pdu's with invalid data
att: Fix sending pdu's with invalid data

When encoding an att_data_list we need to make sure that each element
lenght of the data list will not exceed 255, because that information
will be encoded as a octet later.

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