o Minor bugfixes (address selection):
    - Introduce fascist_firewall_choose_address_ls() which chooses an
      IPv6 or IPv4 address based on a smartlist of link specifiers of
      what is available and what we prefer. We use this function in
      hs_get_extend_info_from_lspecs(). Fixes bug 23588; bugfix on
      0.3.5.1-alpha. Patch by Neel Chauhan.