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