• Attempt to implement IPV6_V6ONLY sockopt wrapper - not all OSes can
  disable it, so detect and skip those
  
• Provide ->sockaddr and ->peeraddr convenience accessors, same as
  IO::Socket::INET (RT75071)
  
• Use new NIx_NOHOST and NIx_NOSERV flags to avoid redundant
  getnameinfo() lookups when only one of host or service name is
  required
  
• Ensure that errno gets set to EINVAL on getaddrinfo() failures