Send ConnDiags event before revalidating network in CS.

This change updates ConnectivityService to notify the
ConnectivityDiagnosticsHandler of app-reported connectivity before
attempting to revalidate the network. This change forces an ordering on
Connectivity Diagnostics events in the case that the reported
connectivity does not match the known connectivity for the network -
this leads to the network being revalidated and the
ConnectivityDiagnostics event onConnectivityReportAvailable. Passing the
onNetworkConnectivityReported event to the
ConnectivityDiagnosticsHandler first ensures that it is passed to
callbacks before any potential ConnectivityReports are.

Bug: 159718782
Test: android.net.cts.ConnectivityDiagnosticsManagerTest
Original-Change: https://android-review.googlesource.com/1350662
Merged-In: Ic7bc7138c54c47bbfdf56af5811709fde66f8606
Change-Id: Ic7bc7138c54c47bbfdf56af5811709fde66f8606