Moved data connection response into system api.

This is a preliminary step for IWLAN refactoring, where data response
will be one of the parameter in data service callback.

Test: Telephony sanity tests
bug: 64132030
Merged-In: I7eb5318cd75ca3b7a29d5bf0da18d6b29a228ee1
Change-Id: I7eb5318cd75ca3b7a29d5bf0da18d6b29a228ee1
(cherry picked from commit e44609b1)