ensure that *all* fields in the req structure are cleared out before reusing...

ensure that *all* fields in the req structure are cleared out before reusing it; has_to_tag was not cleared, which caused the second incoming call over a TCP socket to fail if pedantic checking was enabled


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@148695 65c4cc65-6c06-0410-ace0-fbb531ad65f3