Allow IPv6 addresses to be canonical

In legacy/trac#17604 (moved), we allowed IPv6 connections to set is_canonical_to_peer. But we did not let them set is_canonical.

So channel_tls_process_netinfo_cell() handles IPv6 addresses, but connection_or_check_canonicity() does not.

This inconsistency could be one cause of the logging issues in legacy/trac#24841 (moved).

We should allow IPv6 connections to be canonical. We should also do some cleanup of the related connection address logging in legacy/trac#33898 (moved).

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