Roger Dingledine authored Jan 30, 2018 and Nick Mathewson committed Feb 16, 2018

This commit takes a piece of commit af8cadf3 and a piece of commit
46fe353f25, with the goal of making channel_is_client() be based on what
sort of connection handshake the other side used, rather than seeing
whether the other side ever sent a create_fast cell to us.