End stuck DTMF if AST_SOFTHANGUP_ASYNCGOTO because it isn't a real hangup.

It doesn't hurt to check AST_SOFTHANGUP_UNBRIDGE either, but it should not
be set outside of a bridge.

(issue ASTERISK-20492)
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Merged revisions 381466 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 381467 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@381469 65c4cc65-6c06-0410-ace0-fbb531ad65f3