zmtp: try to downgrade the protocol to talk to a lower protocol peer

[myzhan]

After reading the "Version Negotiation" section of rfc23, I think we can try to work with a lower protocol peer in the future.

See also: https://rfc.zeromq.org/spec/23/

[smeyerhot]

What is the status on this? Can we merge this…

[rgbkrk]

@myzhan would you be interested in reviving this and coming back in as a maintainer?

[myzhan]

@rgbkrk This is not a valid PR, don't merge. And thanks for your invitation, it's hard for me to rewrite all the features in pure go and keep it updated. I prefer to use goczmq.

[rgbkrk]

Cool, I'm using goczmq too. I'm afraid of what it's going to look like when I need to cross compile someday though 😢