Use set_keyset CONNCONF when running conference, during conference the CONFRN button is disabled, whilst the CONFLIST and JOIN buttons are enabled, upon ending the Conference, this is reversed. Fixes #141

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@4876 43c1dc8c-776e-4df2-8ef1-6e829299be21