Sort activeSubscriptionInfoList according to API annotation

SubscriptionManager#getActiveSubscriptionInfoList() should return
sorted list by sim slot index then by subscription id, according to
API annotation in JavaDoc.

Issue:
After SIM swap on DSDS device, tabName of slot1 becomes "UNKNOWN" in
MobileNetworkSettings. When updating tabName, slotId is compared
with activeSubscriptionInfo list one by one in ASCENDING order.
But sometimes activeSubscriptionInfoList is NOT sorted.
In this case, slotId will be unmatched and tabName becomes "UNKNOWN".

Test: manual - Check that display name of subscription is shown
correctly in the tab of mobile network settings.
Bug: 111185160

Change-Id: I67ad0578c1202701dbbca6505458cf529f59570b