implement getFeatureExtension for asterisk >= 12

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@4614 43c1dc8c-776e-4df2-8ef1-6e829299be21
send digits when on monitor feature

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@4615 43c1dc8c-776e-4df2-8ef1-6e829299be21