#3254 Enhancement of NTF notification

[Thanh Nguyen]

When IMM changes an attribute with NOTIFY flag, NTF sends the changed attribute
values and the old attribute values fetched from IMM.
The fetching of old attribute values from IMM might not be successful under a certain condition in which the old values are overwritten before NTF attempts to fetch the old values.

To avoid this situation, IMM will send spontaneously the old attribute values to
NTF.