x/sys/unix: SockaddrStorage "__data" field not exported

[mdlayher]

The current SockaddrStorage type is not useful because the __data field is not exported due to being named X__ss_padding by default when run through the code generator.

In addition, the data type of this field is a either an array of uint8 or int8 on various platforms, which will make it difficult to use.

I will submit a change to export this field as Data and simplify all of the array types to an array of bytes.

See also:
https://go-review.googlesource.com/c/sys/+/106656
https://elixir.bootlin.com/linux/latest/source/include/uapi/linux/socket.h#L14

And a similar workaround applied with:
https://go-review.googlesource.com/c/sys/+/107415

[gopherbot]

Change https://golang.org/cl/108195 mentions this issue: unix: export Data field of SockaddrStorage on Linux