Fix NetworkChangeNotifier on Android to know underlying type of VPN

Fix AndroidRDefaultNetworkCallback.getNetworkState() to return the type
of the network underlying the VPN rather than TYPE_VPN.
getConnectionType(Network) already was able to find the type of the
network underlying the VPN; this change moves this code into
getNetworkInfo(Network) and calls this new method from
getNetworkState(WifiManagerDelegate) and
AndroidRDefaultNetworkCallback.getNetworkState().

Bug: 1208022, 1221052
Change-Id: Ie32aa31f9fc8b0a92b59a27114550c14283f2c90
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2976286


Auto-Submit: Paul Jensen <pauljensen@chromium.org>
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#896457}