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>
Work around https://github.com/google/gvisor/issues/5732
by trying to read /proc/net/route with a larger bufsize if
it fails the first time.
Signed-off-by: Denton Gentry <dgentry@tailscale.com>