Marking nl_pad as public so we can construct sockaddr_nl

[WillYu91]

Addressing issue 1135

#1135

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[gnzlbg]

I suppose that nl_pad are padding bits required for the ABIs to match. I wonder if one shouldn't be using hererepr(align), repr(packed), etc. instead. @alexcrichton ?

[alexcrichton]

repr(align) is fine to use yeah, repr(packed) I believe is still feature gated

[gnzlbg]

Any progress here? @WillYee please use repr(align)/repr(packed)/etc. to remove the padding field instead of making it public.

[gnzlbg]

I'm closing this, since it is intended for this to be an internal implementation detail. See #1135 for how to initialize these structs.