apps/gmr1_rx: Add TCH3 channel follow
apps/gmr1_rx: Add TCH3 channel follow

Simple "follow first TCH"

Signed-off-by: Sylvain Munaut <349f318521b45672c77207abf1a5ed60eb011db1@246tNt.com>

marcelmaatkamp/gnuradio-osmocom-gmr,marcelmaatkamp/gnuradio-osmocom-gmr,marcelmaatkamp/docker-gnuradio-osmocom-gmr,marcelmaatkamp/docker-gnuradio-osmocom-gmr,marcelmaatkamp/docker-gnuradio-osmocom-gmr,marcelmaatkamp/gnuradio-osmocom-gmr