Add logs for changes in capabilities and score

This will be useful for diagnosing default network changes.

Logs may look like, for example :
Update capabilities for net 100 : -NET_CAPABILITY_OEM_PAID+NET_CAPABILITY_TRUSTED
Or :
Update score for net 100 : -POLICY_EVER_EVALUATED+POLICY_IS_VPN+POLICY_IS_DESTROYED

Test: FrameworksNetTests
      manual
Change-Id: Ic4788c599573aae9daeca995b8853800aaaba0b8
6 files changed