mod_sasl2_fast: Fixes to make channel binding work again tls-endpoint isn't a thing that exists. Also, we needed to copy more channel binding state from the primary sasl_handler. Ideally we'd have a cleaner way to do this, but I think that's part of more substantial changes that the SASL API deserves.

This module discards typing notifications sent to a bare host JID,
preventing error replies to be sent. These errors are harmless but can
be annoying sometimes if your client shows them prominently.