Make mMatchSubscriberIds as a NonNull variable

In current design, mMatchSubscriberIds can be null which has the
same meaning with empty set, and is not easy to maintain since it
need more checks for this variable when mSubscriberId is null.
Thus make mMatchSubscriberIds NonNull for the maintenance.

Bug: 238843364
Test: build, FrameworksNetTests
Change-Id: I6cfc529b5f4a39ded8598283ff968f2f4d1bc89f
3 files changed