Cleanups for DataCallResponse

-Simplify the nullability checking.
-Have old constructor call new one.
-Use set logic explicitly for order-independent
 comparisons in hashCode()
-Add additional nullability protection
-Add defensive return of Lists
-Change setInterfaceName() to nullable to allow
 for cases where SetupDataCall fails.

Bug: 285590499
Test: atest DataCallResponseTest
Test: atest IwlanDataServiceTest
Original-Change-Id: I3916fb83ee8a0ef048925d29e6e48fb9a37fdd8a
Change-Id: Id0eeeba7bac576d11b106ab4efceff3c0edc3b54