Changes

RTP: add vty configuration for twjit

This patch is the first step in the series adding the ability to use
twrtp+twjit instead of Belledonne ortp.  twjit requires vty config
for tunable parameters - add this config.  Actual use of this added
config will happen in subsequent patches.

Related: OS#6474
Change-Id: I9ccd060fce8416e01356fccd9ae465a7298a9ce5