1.50.0 switched containerboot from using `tailscale up`
to `tailscale login`. A side-effect is that a re-usable
authkey is now re-applied on every boot by `tailscale login`,
where `tailscale up` would ignore an authkey if already
authenticated.
Though this looks like it is changing the default, in reality
it is setting the default to match what 1.48 and all
prior releases actually implemented.
Fixes https://github.com/tailscale/tailscale/issues/9539
Fixes https://github.com/tailscale/corp/issues/14953
Signed-off-by: Denton Gentry <dgentry@tailscale.com>