Prop 312: 5.1. Test Relay IPv6 Addresses Discovery using Chutney

Test the IPv6 ORPort Address Detection changes in proposal 312, using chutney networks.

Since chutney runs on private addresses, these tests might be difficult to write, or they might not tell us much about how tor relays behave on the public tor network. So we shouldn't spend much time on them.

See proposal 312, section 5.1: https://gitweb.torproject.org/torspec.git/tree/proposals/312-relay-auto-ipv6-addr.txt#n1461

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