Personal preference (so it's obvious it's not a bool flag), but it
also matches the --state= before it.
Bonus: stop allowing PORT to sneak in extra flags to be passed as
their own arguments, as $FOO and ${FOO} expand differently. (${FOO} is
required to concat to strings)
Change-Id: I994626a5663fe0948116b46a971e5eb2c4023216
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>