Mock SubscriptionManager in CSTest

KeepaliveStatsTracker calls addOnSubscriptionsChangedListener from the
constructor.
And KeepaliveStatsTracker is instantiated from ConnectivityService
constructor.
So using actual SubscriptionManager leaked listener and tests started
failing.

Bug: 329365833
Test: atest ConnectivityCoverageTests
Change-Id: I65ac34e4bc6b5fd86a290706be844914d09918a5
1 file changed