Cellular Network Infrastructure

Found with repo-install-test, while adjusting it to run more services:

1. osmo-e1d default config is only in /usr/share/doc/osmo-e1d/examples/osmo-e1d.cfg, but should also be in /etc/osmocom where the systemd service looks for it. (this error is at least in the centos package)

2. osmo-ggsn default config conflict (with osmo-gtphub?):

Dec 07 10:10:49 localhost.localdomain osmo-ggsn[21245]: <000d> gsn.c:520 addr(127.0.0.2:2123) bind(fd1c=10) failed: Error = Address already in use

Fixing those should be trivial, but I'll finish up #5365 first.