Regenerate vhost_binding.rs and move custom changes in another file

[stefano-garzarella]

In a PR #185, we fixed some new clippy warnings, but there is one related to __IncompleteArrayField that should be auto-generated by bindgen.

We used an old version that generated also Copy/Clone implementations, but now it looks like they removed it: rust-lang/rust-bindgen#1431

@jiangliu agreed on regenerate it with a new version of bindgen.
We also modified a bit the vhost_binding.rs generated file, so it may be better to move the new struct in another file, so we can update it easily next time