This was missing in the earlier f5eac39ea7 and meant that tsnet users weren't
getting (all of) acme support.
Thanks to @ChaosInTheCRD and @BeckyPauley for debugging.
Updates #12614
Updates #20252
Change-Id: I176a7b179b2ad3726aca484057f0aae7cc3561c8
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>