Rearrange sockaddr_storage padding/alignment fields on Linux and Fuchsia

[stevenengler]

Part of #3004.

Previously on Linux, the sockaddr_storage structure had padding bytes between the ss_family and __ss_align fields. The __ss_align field has now been moved to the end of the structure to eliminate these padding bytes, matching recent glibc versions: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/bits/socket.h;h=4f1f810ea1d9bf00ff428e4e7c49a52c71620775;hb=c804cd1c00adde061ca51711f63068c103e94eef#l190

After the PR on Linux x86-64:

print-type-size type: `unix::linux_like::sockaddr_storage`: 128 bytes, alignment: 8 bytes
print-type-size     field `.ss_family`: 2 bytes
print-type-size     field `.__ss_pad2`: 118 bytes
print-type-size     field `.__ss_align`: 8 bytes

These moved fields are private but they are used in the sockaddr_storages PartialEq, Debug, and Hash implementations, so the exact behaviour may change slightly, but I don't think anyone should be depending on this.

(It looks like Fuchsia has the same issue, but I didn't modify its structure because I don't know much about it, or how to test it.)

[rust-highfive]

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) soon.

Please see the contribution instructions for more information.

[asomers]

I think Fuchsia's definition is here, and yes I think you should fix it in libc.
https://fuchsia.googlesource.com/fuchsia/+/refs/heads/main/zircon/third_party/ulib/musl/include/sys/socket.h#376

[stevenengler]

I think Fuchsia's definition is here, and yes I think you should fix it in libc. https://fuchsia.googlesource.com/fuchsia/+/refs/heads/main/zircon/third_party/ulib/musl/include/sys/socket.h#376

Added a fixup commit to change Fuchsia's definition.

[JohnTitor]

The upstream change is old enough and looking at #1412 and https://github.com/bminor/glibc/releases/tag/glibc-2.26, we could assume the effect is quite limited.

[JohnTitor]

@bors r+

[bors]

📌 Commit 7bbbfb0 has been approved by JohnTitor

It is now in the queue for this repository.

[bors]

⌛ Testing commit 7bbbfb0 with merge 855a6fc...

[bors]

☀️ Test successful - checks-actions, checks-cirrus-freebsd-12, checks-cirrus-freebsd-13, checks-cirrus-freebsd-14
Approved by: JohnTitor
Pushing 855a6fc to master...