WiFi unit test: mock static methods of SubscriptionManager properly.

The following static methods are mocked by using ExtendedMockito:
SubscriptionManager.getDefaultDataSubscriptionId()
SubscriptionManager.getDefaultSubscriptionId()

Bug: 128966900
Bug: 128949241
Test: Unit tests for Wifi: frameworks/opt/net/wifi/tests/wifitests/runtest.sh
Change-Id: I88bf7fdf86eb9d49e03c33404b0e8e958ecf0b38
1 file changed