Changes

ggsn: README: document how to run with testenv

It is possible to run the GGSN testsuite in a lot of ways (as it was
ported from docker-playground, which had the same variations but with a
less consistent way of running them).

Document how it is typically run for development / in jenkins. This
should make it easier for users, in addition to testenv already telling
which configs are available if trying to run the ggsn testsuite without
the -c argument, and to the general help output in "./testenv.py run -h".

$ ./testenv.py run ggsn
[testenv] Using testsuite ggsn_tests (via alias ggsn)
[testenv] Found multiple testenv.cfg files:
[testenv]  * testenv_open5gs.cfg
[testenv]  * testenv_osmo_ggsn_all.cfg
[testenv]  * testenv_osmo_ggsn_v4_only.cfg
[testenv]  * testenv_osmo_ggsn_v4v6_only.cfg
[testenv]  * testenv_osmo_ggsn_v6_only.cfg
[testenv] Select a specific config (e.g. '-c open5gs') or all ('-c all')

Change-Id: I49421151b199fa6536da784b6c412b03f3fdbd05

library/GTPv1C_Templates: Lots of improvements in template declarations

Also most the compiler warnings are fixed, only some which require
special more complex attention are left as is.

Change-Id: I38a4b1c5874fda173a7b89122c84cb83ac71a036

cosmetic: library/GTPv1C_Templates: remove extra indentation level

The extra first indentation level around 99% of the file just loses
space which makes it difficult to keep templates at an acceptable width.
Do similarly to what we already do in lots of other template files which
were added later than this one.

Change-Id: I87755ec0a9023e79fb5f7a40c6c1734dca44696b

library/GTPv1C_Templates: Clean up PCO templates

* Define a generic ProtoElem template and use it everywhere.
* User superset instead of "*, tr_..., *" construct.

Change-Id: I005a6dea0606bcb677260f85b24396b55a150153

mgw: Remove unneeded dep IPCP_Types.ttcn

Change-Id: I318f4ba78adf778820e8d65d5932e454bc5da670

s1gw: Remove unneeded dep IPCP_Types.ttcn

Change-Id: Iad81c8d76efa2618ca7e354d2b73617a54a8d5ee

library: Move IPCP templates GTPv1C_Templates.ttcn -> IPCP_Templates.ttcn

We already have an IPCP_Types.ttcn, and the GTPv1C_Types from
ProtocolModules dep we use doesn't actually specify any record for IPCP,
so those are totally protocol independent.

Change-Id: I233292ea886e1b69a2f9aa1a159c816791b47136

library/PCO_Types: Drop unused nonsense enum

That enum is PAP related, plus it doesn't really match the section
describing, plus it's not used anywhere.
Looks like a development artifact which was not dropped during submit.

Change-Id: Ic791d20dd600b039daa2abef7fa25aaa6780a448

library/PCO_Types.ttcn: Drop unsued IPCP_OPT enum

It is unused, plus IPCP_Types.ttcn already defines a more complete enum
in IpcpConfigOptCode.

Change-Id: I867ab36063db262b46fc4546c17a902699a6e37c

ggsn: Introduce test TC_pdp4(6)_act_deact_mtu

This tests so far only test retrieval of MTU over PCO, which is only
used for IPv4 APNs.
When IPv6 is in used, it is expected to be retrieved over IPv6 SLAAC RA.
Such tests will be done in a follow-up patch once the related procedure
is implemented in osmo-ggsn.

Related: OS#6298
Related: SYS#7122
Change-Id: I2ceb76a3a07b44f69937c9f5a040482320bca377

ggsn: Validate MTU sent during ICMPv6 RA

Related: OS#6298
Related: SYS#7122
Change-Id: Ia5bbc5f9e42b02d1b9bd6c4190a2bd439663deeb