Wait for default route for wifi check

Instead of only waiting for an IPv6 address, wait for global IPv6
addresses to be routable.

This mirrors the check used for AI_ADDRCONFIG in DnsResolver. Without
this, the later call to network.getAllByName may only return IPv4
addresses if IPv6 global addresses are not reachable.

Test: atest
Change-Id: I2cedd58431eb8abeb5ffd9fb8daedb061586373b
1 file changed