Fix sccp_conference_hold/sccp_conference_resume

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@4881 43c1dc8c-776e-4df2-8ef1-6e829299be21
Set the correct keysets during channel_hold/channel_resume when dealing with confence. During new call, put conference on hold as well

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@4882 43c1dc8c-776e-4df2-8ef1-6e829299be21
Cleanup sccp_feat_join (handle error cases / use resume swap)

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@4883 43c1dc8c-776e-4df2-8ef1-6e829299be21