Added traffic descriptor for default data profiles

The default data profile have null traffic descriptor. They
should have DNN, which is same as APN, in the traffic descriptor.

Fix: 229180871
Test: atest DataProfileManagerTest
Merged-In: I4a0e639376b68a7669ca2898db56fd0fcebd51a2
Change-Id: I4a0e639376b68a7669ca2898db56fd0fcebd51a2