Closes #1094 .

Closes #1304 .

Closes #1178.

This was added in Linux 5.1 and will only show up in the next glibc
release, thus skip in tests.

`nl_pad` field does not contain any actual data, so using it for
comparison or hashing doesn't make sense. Instead manually implement
extra traits ignoring this field.

The `pad` or `__reserved`  fields are not always 0 on some platforms,
so when used in the `PartialEq` implementation being used, fails some
comparisons. This commit manually implements the extra traits to
correct this behavior.