When choosing an orport from an extendinfo, pick randomly.

(This is not fully general yet: we only pick randomly among supported addresses, and each extendinfo contains at most one IPv4 address and at most one IPv6 address, no matter what the extend cell had.)

This change will help dual-stack relays do IPv6 reachability tests, in theory, by having them sometimes do IPv4 connections and sometimes do ipv6 connections.

Closes #33220 (closed).