Use ClientIPv4 and ClientIPv6 to select a bridge address

If a bridge has an IPv4 and an IPv6 address, and a tor client knows both, it should select the address family based on the values of:

• ClientUseIPv4
• ClientUseIPv6
• ClientPreferIPv6ORPort ?

(I don't think ClientPreferIPv6DirPort is relevant here.)

This code works as-is, so I don't see any reason to change it urgently.