Make getNetworkInfo() take into account VPN underlying networks.

If a user is subject to a VPN, getActiveNetworkInfo() will return
the VPN's underlying network (e.g., TYPE_WIFI), so that apps that
call getActiveNetworkInfo to answer questions like "is the device
connected to wifi?" will continue to work. Make getNetworkInfo
do this as well: if the query is for a network type that is
underlying the current user's VPN, then return that network.

Bug: 19196545
Change-Id: Ic5a651735b927c758594a26d26a03fbd704b52e6