SyncSM09: Add Callback to UpstreamNetworkMonitor

Instead of passing state machine to UpstreamNetworkMonitor, wrapped it
by an interface would have two benefits:
1. Easier for testing.
2. Isolate state machine operation in callback.

Test: atest TetheringTests
Change-Id: I2a97fd5cbc8c49df8c3c98428c6570916ab31ea5