What is the consideration of not turning on --accpet-routes by default

[utas-zyan]

First of all, quite appreciate the work you have done.
Just wondering if we can turn on --accpet-routes by default, or add environment variables to toggle it.

From tailscale point, their default behaviour is also different across the platform -- which I am not 100% sure why, most likely for security considerations.

This is just a opinion query so no PR had bene raised for it... but should be just a 1/2 lines of change of code.

[metaskills]

Love it. Swing away. Would gladly take that PR.