findIPv4DefaultRoute() is removed from Vpn, so IllegalStateException is no longer thrown for IPv6 only networks. The test testStartLegacyVpnIpv6 is now not testing anything new and so it is removed. Note that other tests that will be calling startLegacyVpn() ensure coverage is not lost. Bug: 161776767 Test: atest FrameworksNetTests Change-Id: I6ac9d7c196b7bc4c44fc2ad32baa25b106640ef4