Fix: Transfer using 6921 (Reported/Patched by Antonio)

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5717 43c1dc8c-776e-4df2-8ef1-6e829299be21
Enhancement: Synchronized setCalled/setCalling/setOriginalCalled/setOriginalCalling party funcions.

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5718 43c1dc8c-776e-4df2-8ef1-6e829299be21
Fix: Allow calledparty/callingparty to be overwritten using an empty string during connectedline update. (Issue & Adapted Patch by Antonio).

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5719 43c1dc8c-776e-4df2-8ef1-6e829299be21