unsz was always exactly '1' here due to an unfortunate mispositioning
of closing parenthesis. While it's generally irrelevant because bind(2)
is passed the (accurate) sep->se_ctrladdr_size instead, it's not very
helpful for anything locally that wants to use it rather than assuming
that sep->se_ctrladdr_size perfectly fits the end of sun_path.
Just drop unsz entirely and use the result of SUN_LEN() for it.
MFC-after: 3 days
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