Using Context#getSystemService instead of ServiceManager#checkService

ConnectivityService is going to be a mainline module, it can only
use formal APIs or @SystemApi. So use public API -
Context#getSystemService() instead of hidden API -
ServiceManager#checkService().

Bug: 170598012
Test: atest FrameworksNetTests
Change-Id: I9824caa7aec57e70f0ba405fcce39f9bc068732d
2 files changed