IPv4 routes known by Link Properties

com.android.internal.telephony.DataCallState only has the IPv6 default gateway, so that's all android.net.LinkProperties gets. This is a problem for PPTP VPN accounts, which wants an ipv4 default route from LinkProperties.

Without an ipv4 default route in the LinkProperties object, pptp fails in com.android.settings.vpn2.VpnSettings.getDefaultNetwork with the exception: java.lang.IllegalStateException: Cannot get the default gateway