actix-http::ws: Remove redundant + 4 byte reservation when masked

[asonix]

PR Type

Bugfix

PR Checklist

• [ ] Tests for the changes have been added / updated.
• [ ] Documentation comments have been added / updated.
• [x] A changelog entry has been made for the appropriate packages.
• [x] Format code with the latest stable rustfmt.
• [ ] (Team) Label with affected crates and semver status.

Overview

I noticed the mask caused a +4 to apply twice, once on line 175, and once again when reserving space