GTP-U sequence numbers are enabled unconditionally
In order to support and test all possible configuration, it should be possible to disable GTP-U sequence numbers on both the GGSN as well as the sgsnemu side.
- % Done changed from 20 to 80
See https://gerrit.osmocom.org/#/q/project:osmo-ggsn+topic:gpdu-seq and specifically
pending some automatic testing for with/without seq-nr on both sgsnemu and ggsn side.