deliver events with the core thread pool set events-use-dispatch=true in switch.conf.xml to use the old way

Conflicts:
	src/mod/endpoints/mod_sofia/sofia.c

FS-4757 this should fix it but I am not happy with the way this is done but since polycom is one of the only phones that does this right I have no other choice

* Rename option ringback-during-collect to immediate-ringback
* Allow regular ringback tone with immediate-ringback, not just a wav file
* Do not request full frame of data, just packet_len which is what we receive per IO interval
* Ignore user data when playing ringback tone