Add channel check for getter/setter macro. Removed .setChannelTechPVT because it is/was not used nor implemented

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5065 43c1dc8c-776e-4df2-8ef1-6e829299be21
Fixes Speakerphone dropping (fixes #172)

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5066 43c1dc8c-776e-4df2-8ef1-6e829299be21