We used to use "redo" for that, but it was pretty vague.
Also, fix the build tags broken in interfaces_default_route_test.go from
a9745a0b68, moving those Linux-specific
tests to interfaces_linux_test.go.
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
IPv4 and IPv6 both work remotely, but IPv6 doesn't yet work from the
machine itself due to routing mysteries.
Untested yet on iOS, but previous prototype worked on iOS, so should
work the same.
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>