Skip unreachable route when estimating VPN destinations

Bug: 122652441
Test: atest com.android.server.connectivity.VpnTest
Test: Establish a IPv4 VPN with minimal routes and check
(dumpsys connectivity) the VPN network does not have INTERNET
capability.

Change-Id: Ic7f19ebb7b7f78a6ffb2a8ec3fc3eca5e5421f57
2 files changed