require only ipv4 or ipv6 success for sendQuery success

[mbver]

serf's TestCommandRun_mDNS on my macOS M1 fails because sendQuery fails due to:

    _, err = c.ipv6UnicastConn.WriteToUDP(buf, ipv6Addr)

this will fail because the ipv6 multicast connection doesn't bind to a specific interface.

	ipv6List, _ := net.ListenMulticastUDP("udp6", config.Iface, ipv6Addr)

in this case config.Iface is nil.

however, this is successful

	_, err = c.ipv4UnicastConn.WriteToUDP(buf, ipv4Addr)

even though ipv4List is created with nil iface. multicast works for ipv4 at lo0 interface and it doesn't require specific interface binding.
sendQuery should be considered success with just one successful send. if it is successful on ipv4 but unsuccessful on ipv6, it's ok to proceed. if it is unsuccessful on ipv4 but successful on ipv6? that's unlikely, but still ok to proceed.