IMS: Update data rat in IMS phone service state.

Keep the data rat information in Ims phone servicestate updated
with that from default phone.
This makes sure applications can query correct data RAT when
default phone is not registered to voice and ims is in service.

Change-Id: I8161a43efe9408572d41d7a0a320972873a7e60c
CRs-Fixed: 792462