[Reviewer: Rob] Add support for protocol independent (IPv4/IPv6) table indices based upon RFC 4001.

I believe this is a way to move forward from the IpAddress table indices used in the current MIB. I'm not sure it is the best way. It is more of an experiment, and a place to start the discussion of how to proceed.
It should do the right thing… leave the address type as unknown. But, it is not as clear as it could be as you point out in the next comment. I’ve added the else clause to clarify the intent. I agree there is not a good mechanism to log a failure here other than syslog. It did not seem like that was warranted given this is a closed ZMQ interface which should contain a valid IPv4/IPv6 addresses. I do not think a bracketed address should show up on the interface in this context since that is typically only used when a port is added to the address?