RFC 2361 section 24.4.1 send a 400 Bad Request if the request
can not be understood due to malformed syntax. Currently we
simply ignore a packet with a missing callid, to, from, or
via header. Instead of ignoring we now send the 400 Bad request.
git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@272981 65c4cc65-6c06-0410-ace0-fbb531ad65f3