it has been deprecated in libosmocore.git 2.5 years ago:
commit 7e0686c6b4b456ec4e6e15689694b1bcf96c301f
Author: Neels Hofmeyr <neels@hofmeyr.de>
Date: Mon Sep 10 20:58:52 2018 +0200
Change-Id: Ia6946fae497319a894d4e664ac8642340620822e
Configure each osmo-* program to send GSMTAP log output to the IP of the
docker container, which runs the testsuite (and therefore runs tcpdump).
Related: https://lists.osmocom.org/pipermail/openbsc/2019-June/012946.html
Change-Id: I99e74f6ffb5b7d566cec35995bf067df414968d8