consensus-formats: formatting of router items up to and excluding `s`

s is done in !324 (merged), so stopping this branch here.

spec/dir-spec/consensus-formats.md

@@ -587,7 +587,8 @@ or `0` for "none".
 The first advertised IPv6 address for the OR,
 if it is reachable.
 
-Present only if the OR advertises at least one IPv6 address,
+Present only if the OR advertises at least one IPv6 address
+in its server descriptor,
 and the authority believes that
 the first advertised address is reachable.
 Any other IPv4 or IPv6 addresses should be ignored.