[sd] always publish on non-loopback addresses

[sd] always publish on non-loopback addresses

When adding support for service discovery publishing as a sidecar, I realized that health probes are often performed against the loopback address, but the sd libraries don't support separate addresses for probing and publication.

This commit adds that by detecting the local primary IPv4 and IPv6 addresses when the probe address is a loopback IP.

Supporting changes:

- Add `net2` library with `MyIP4()` and `MyIP6()`

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