So wgengine/router is just the docs + entrypoint + types, and then
underscore importing wgengine/router/osrouter registers the constructors
with the wgengine/router package.
Then tsnet can not pull those in.
Updates #17313
Change-Id: If313226f6987d709ea9193c8f16a909326ceefe7
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>