Early fix to requestHangup issue reported by Pavel / Niklas, actual fix is still being worked on.

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5543 43c1dc8c-776e-4df2-8ef1-6e829299be21
Added force_dtmfmode for people running earlyrtp=immediate and being faced with misbehaving phones (some 7960) during redial and/or onhook dialing, whereby DTMF frames come in in the wrong order (Reported by Pavel). Default setting for force_dtmfmode remains AUTO and should only be changed when absolutely necessary (i.e. Experienced users)..

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5544 43c1dc8c-776e-4df2-8ef1-6e829299be21