R1:6058d3305f82

Normalize remote IP addresses when writing to logs, etc

Summary:
Ref T11939. IPv4 addresses can normally only be written in one way, but IPv6 addresses have several formats.

For example, the addresses "FFF::", "FfF::", "fff::", "0ffF::", "0fFf:0::", and "0FfF:0:0:0:0:0:0:0" are all the same address.

Normalize all addresses before writing them to logs, etc, so we store the most-preferred form ("fff::", above).

Test Plan:
Ran an SSH clone over IPv6:

```
$ git fetch ssh://local@::1/diffusion/26/locktopia.