relay: Allow RFC1918 addresses for non public relays

In other words, if PublishServerDescriptor is set to 0 and AssumeReachable to 1, then allow a relay to hold a RFC1918 address.

Reasons for this are documented in #40208 (closed)

Fixes #40208 (closed)

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