Filter response address records by network interface

[cyanfish]

Per https://datatracker.ietf.org/doc/html/rfc6762#section-6.2:

When a Multicast DNS responder sends a Multicast DNS response message
containing its own address records, it MUST include all addresses
that are valid on the interface on which it is sending the message,
and MUST NOT include addresses that are not valid on that interface
(such as addresses that may be configured on the host's other
interfaces).

I have this mostly working in my fork but I'm not sure it's the best way to handle this.

[jdomnitz]

I agree this will need some work but it's worthwhile. I'll work through some other concepts. This is the last area I've found where not complying with the standard causes problems.

[jdomnitz]

Reference here: richardschneider#25

Current Issues:

• IPv6 queries should return IPv4 addresses and vice-versa (They may be routable)
• Removing all but the sending NIC breaks support for multi-homing and shared services
• This only works with semetric routing

Easy first steps:

• Loopback addresses are never routable externally
• Update service records in all instances where they may change (WIP)

TBD - How does mDNSResponder handle this?