hermit: add/fix AF_* values

[mkroening]

Description

This PR

• adds AF_UNSPEC,
• adds AF_VSOCK, and
• makes AF_INET = 3

on Hermit.

Sources

See hermit-os/kernel/src/syscalls/socket.rs#L27-L31 for reference and hermit-os/kernel#1640 for details on the AF_INET change (POSIX requires AF_UNSPEC = 0 and distinct values for AF_*).

Checklist

• Relevant tests in libc-test/semver have been updated
• No placeholder or unstable values like *LAST or *MAX are
  included (see #3131)
• Tested locally (cd libc-test && cargo test --target mytarget);
  especially relevant for platforms that may not be checked in CI

[rustbot]

r? @tgross35

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[tgross35]

Thanks!

@rustbot label +stable-nominated