use unknown reason for call request

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@4203 43c1dc8c-776e-4df2-8ef1-6e829299be21
fixes #18, with room for improvement (transferer callLog)

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@4204 43c1dc8c-776e-4df2-8ef1-6e829299be21