Changes

ggsn: Split test and relax expectations testing gtpu access over ipv6 ll-addr

Testing gtpu traffic to some potentially external IP address using the
link-local address has no clear usecase and it also depends on the
network setup and the implementation of the GGSN.
Hence, remove it from the regular test and move it to another test which
has a relaxed validation accepting different resolutions.
This allows knowing/testing the code path in the GGSN, while accepting
different outcomes.

Related: OS#6382
Change-Id: Icfae181ba1bb0dfb8a1a15dfe3a1d542ce69d88a

sgsn: Fix running with testenv.py podman setup

The initial testenv.py setup introduced in osmo-ttcn3-hacks.git
6baec93cb85fa8a0051e9aacd0178e90adbfdadc lacked some recent updates to
the ttcn3 testsuite setup where a second IP address is added to the
container in order to distinguish between RNC and CN in GTPU.

Change-Id: Ia0af52f8b7d61c15bdf2b6152fae27dd003d00e8

sgsn: Introduce test TC_attach_rau_a_b_wrong_old_ra

This test reproduces a crash in osmo-sgsn, and fixed in
osmo-sgsn.git Change-Id I5a4328c6e945b85dd815215724feecadba59c435.

Related: OS#6441
Change-Id: I3ce02f30a1e5becb80ab2a29f6bf5d08dd45b79c