Make sure we start incoming calls on SS7 with echo cancellation enabled. Also...

Make sure we start incoming calls on SS7 with echo cancellation enabled.  Also make sure when completing a COT we call ss7_start_call with the proper locks held.  Lastly, make sure if we fail to get a channel from zt_new that we don't assume it's there.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@114092 65c4cc65-6c06-0410-ace0-fbb531ad65f3