TetheringTest: improve onUpstreamCapabilitiesChanged test

This is a preparation for migrating the upstream change notification.

Changes:
1. Modify testUpstreamNetworkChanged
   - Add losing upstream test
   - Verify the capabilities on the explicit network
2. Modify testUpstreamCapabilitiesChanged
   - Verify the capabilities on the explicit network
3. Add testUpstreamCapabilitiesChanged_stopTethering
   - Test that TetherModeAliveState#exit sends the null upstream
     notification. Above tests only covers the notifications which
     are triggered by chooseUpstreamType or EVENT_ON_CAPABILITIES.

Bug: 243516306
Test: atest TetheringTest

Change-Id: I8f5b23f93c27b8c690b2fd275e3f636fbaeb4973
1 file changed