Heavier network extensions might require the wireguard-go component to
use less ram, so let users of this reduce these as needed.
At some point we'll put this behind a configuration method of sorts, but
for now, just expose the consts as vars.
Requested-by: Josh Bleecher Snyder <josh@tailscale.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
