update setsockopt error set according to POSIX
update setsockopt error set according to POSIX

In the code review I accidentally encouraged Luna to remove some
handling of errors that are possible according to POSIX, but I think how
Luna had it before was better, so I fixed it, and now the branch should
be good to merge.

raulgrell/zig,raulgrell/zig,raulgrell/zig,zig-lang/zig,zig-lang/zig,andrewrk/zig,raulgrell/zig,zig-lang/zig,andrewrk/zig,raulgrell/zig