UDPLITE support

[dtaht]

Somewhat related to #350 is UDPLITE. It's supported on many an OS (linux and bsd for sure), and by default behaves just like UDP, with the exception that you can shorten the checksum, which is increasingly not terribly useful for its intended purpose, but it's there...

I'm getting kind of concerned about UDP getting so heavily used by QUIC, limited port space from CGNATs, etc, and it's always seemed to me that at least trying to make udplite work was rather straightforward, and only a couple lines of code.

https://en.wikipedia.org/wiki/UDP-Lite

[Thomasdezeeuw]

Prs would be welcome.

[dtaht]

Noted. Whenever I get better at rust.

[Thomasdezeeuw]

@dtaht you can take a look at #359 and try to copy and modify it for UDPLITE.

[dtaht]

It is even simpler than that. This is all there is to it, in C:

   sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDPLITE);