netdoc: Call shrink_to_fit() when we're done parsing rs sections

(Once we're done parsing these, the vector will never get any
longer.)

crates/tor-netdoc/src/doc/netstatus.rs

@@ -1326,6 +1326,7 @@ impl<RS: RouterStatus + ParseRouterStatus> Consensus<RS> {
             }
             relays.push(routerstatus);
         }
+        relays.shrink_to_fit();
 
         let footer = Self::take_footer(r)?;