Replaced sccp_channelstate_t with sccp_earlyrtp_t for use by earlyrtp. Introduced new earlyrtp state, called 'immediate', which will force overlap dialing immediately when picking up the receiver. For use by experienced asterisk users only (requires special dialplan precautions) (Patch created in coorporation with Pavel Troller).

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5502 43c1dc8c-776e-4df2-8ef1-6e829299be21