zeroconf: fix an issue concatenating bytes and str `bytes(length)` doesn't do what we want, so use `str`. There appear to be a ton more issues in this extension, including: - globals()[b'_GLOBAL_DONE'] using bytes as the key - `__author__` and similar using bytes - `BadDomainName` is feeding bytes to the Exception constructor - DNSRecord.toString() has the wrong signature (should be str, not bytes) Differential Revision: https://phab.mercurial-scm.org/D11303