Adding constant SOMAXCONN to vxworks

[biabbas]

Hi all, I'm just adding the SOMAXCONN variable that was missing in the VxWorks Rust libc. I've checked the libraries, and this is the correct value for the constant.

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @JohnTitor (or someone else) some time within the next two weeks.

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[biabbas]

Thank you. When will this be reflected in crates.io pulled crate?