For instance, ephemeral nodes with only IPv6 addresses can now
SOCKS5-dial out to names like "foo" and resolve foo's IPv6 address
rather than foo's IPv4 address and get a "no route"
(*tcpip.ErrNoRoute) error from netstack's dialer.
Per https://github.com/tailscale/tailscale/issues/2268#issuecomment-870027626
which is only part of the isuse.
Updates #2268
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
