There is a good amount of repetition in the two frame handling routines
in the Dial API. This commit combines the two functions into one.

This is in preparation for an upcoming commit that adds the ability to
handle frames for a channel in a bridge.

ASTERISK-25925
Reported by Mark Michelson

Change-Id: Iaae2f174e3058e774cb44e10659fcdfb85345c58