ConnectivityService: safer locking

This path changes a dangerous lock path in reportNetworkConnectivity().
This methods is called outside of the main ConnectivityService handler
and takes a lock on a specific NetworkAgentInfo whose connectivity
status is being reported.

While this lock is held, reportNetworkConnectivity() goes on and query
the network policy state for that network, which may ends into
NetworkPolicyManagerService.

Instead, the lock on NetworkAgentInfo is only held long enough to make a
copy of LinkProperties, which is then passed to
NetworkPolicyManagerService without that lock.

Bug: 36902662
Test: could not repro b/36902662, reportNetworkConnectivity() works.
      $ runtest frameworks-net

Change-Id: Iac4b75bcecbdddb0ac695c8b1a87ae755f62f47f