support dgram unix socket

[flisky]

such as imuxsock from rsyslog

[dndx]

Thanks for your contribution! Can you please provide test cases for this addition inside t/sanity.t similar to TEST 2?

[flisky]

I'll try it in next few days.

[flisky]

Testcase added.

A known issue -
the directive udp_reply is required, but we won't call sock:receive(), so the following warning occurs:
WARNING: udp server failed to send reply: Connection refused

Is it acceptable for us? @agentzh, @dndx, Any thoughts on this？

[geemang2000]

👍

[calio]

@dndx can you take a look?

[flisky]

I think maybe @p0pr0ck5 intersted? Thx,