Make sure IPv6 ORPorts are configured

Our exit-v6.tmpl should always have a v6 ORPort.

Furthermore, bridges+ipv6-min network configuration now uses v6 authorities and a v6 Exit. Without this, the IPv6 bridge self rechability test would never work.

Closes #40007 (closed)

Signed-off-by: David Goulet dgoulet@torproject.org