Add Codec Column to main interface

[pksml85]

Hi Kaian. I am doing some codec analysis and it would be very helpful to have a column option for the agreed-upon codec in SIP invite dialogs. This would save me from having to inspect each dialog individually to see which codec was used.

For example, the last SDP message from the dialog has this data:
m=audio 19064 RTP/SAVP 9 101
a=rtpmap:9 G722/8000
a=rtpmap:101 telephone-event/8000

My feature request would be for a Codec column option on the main interface on sngrep that would show something like 9/G722/8000.
(I assume that the last SDP message would be the most accurate, considering the possibility of late-inbound negotiation.)

Perhaps this column would be populated only for COMPLETED dialogs, since CANCELLED/BUSY dialogs do not have a completed codec exchange between both parties.

Thanks for your consideration!