Add RTP payload type for G726 codec
Replacement MR for !682 (closed) as we don't have access to the original branch.
Airoha uses RTP payload type "80" for G726 codec, which is different from the default type "2" used by asterisk-chan-voicemngr.
asterisk-chan-voicemngr uses ubus call endpt codecs to retrieve the RTP payload type and apply it.