Remove some usage of the old CI sshConnection class

Set SA mode as default

- Set standalone (SA) mode as the default.
- Adjust commands in Docker Compose files by removing --sa flags and
  adding --nsa flags where applicable.
- Add a function to verify that only one mode is being used at a time.
- Update all relevant documentation.

CI: Remove 5g_l2sim files

Delete the XML, conf, and YAML files related to the RAN-L2-Sim-Test-5G pipeline
that has already been removed.

In the last commits, SSHconnection class has been removed from
cls_containerize.py. We therefore don't need the username and password,
as cls_cmd uses certificates only. Remove the usage of the username and
the password, and harmonize the use of GetCredentials().

Recent refactoring replaced the CreateWorkspace function call with a
dedicated XML step (for clarity, and because it avoids needless
recreation of workspaces). In the proxy function, the same
CreateWorkspace xml step has been added, cloning the OAI RAN repo, when
we actually need the repository for the proxy. Hence, fix this by
calling the CreateWorkspace() function manually, but only when
necessary, to build the proxy. (It would only be a problem if the
pipeline would rebuild the proxy, which did not happen because not much
work is happening on the proxy repo).

Further, refactoring and simplication of the proxy build function were
done:

- never tag proxy with develop, that makes no sense
- overwrite CreateWorkspace() info after having created and used the
  workspace (the "if" to build the proxy)
- simplify copying of logs
- add simple unit test
- remove check for ubuntu; the dependcy is "docker". Simplify the code
  to not obscure with a class variable.

The first thing Build_Proxy does is to remove the repository. Further,
Build_Proxy does not use the OAI RAN repo, but the proxy repo. The
Create_Workspace() is therefore completely useless.

Remove CheckAndAddRoute(), as it is complicated to read, uses a
multitude of hostname/IP/password combinations. Replace with scripts on
the machines, which, as of this commit, are:

- porcepix: ~/after-reboot.sh
- ofqot: ~/after-reboot.sh
- nepes: ~/after-reboot.sh
- obelix: ~/how-to-resetup-obelix-out-of-reboot.sh

It is clearer in CI logs to use absolute paths, and that is also a
"preference" of the new SSH class (cls_cmd.py) in the sense that some
functions don't handle "cd" gracefully (because of underlying Python
library paramiko).

For zip, though, we should change to have nice relative paths in the
archives, so use cd <path> && zip ... to achieve that, instead of
changing to a directory. This way, the path on which we operate is still
visible in the logs in each line.

THere are four possibilities, for the three options (phy_test, do_ra,
nsa):

- None is set -> SA
- Only one is set of each -> corresponding mode

Introduce a function softmodem_verify_mode() to check for these.

fix blocking bugs in command nr_dlsim -n100 -e27 -s35 -b 273 -R273 -x4 -y4 -z4

errors in main OAI code:

- one stack overflow
- one variable array of size 0
- one direct usage of unaligned SIMD

and small fixes inside the tests tool nr_dlsim to handle this large configuration (4layers, 100MHz)

use a better complex vector multiplication function

Since commit 041b2b2d, the CI main loop
iterates over all steps, even if there has been a problem during an
earlier XML step. In all cases, UndeployObject() is marked to always
run, as we always need to make sure that all deployed services are
terminated. UndeployObject() always recovers logs. Hence, it's not
necessary to do it here as well; it leads to duplicated logs.

This is visible in all pipeline with a failed deployment: the logs
appear twice.

create_workspace.sh used to check out develop by default. However, this
is unnecessary because the script later checks out a specific reference
(which can be a commit ID, which is not accepted by git clone, the
reason we don't check out during clone); the repository will simply be
empty in the beginning, which should not be a problem.

Further, it is problematic because we use this script for the build of
the L2sim proxy, and the repository does not have develop; thus, without
this modification, L2sim proxy build will always fail.

Following up on !3081 (comment 140856)

and simplify a bit (DevAssert instead of goto/exit)

and simplify a bit (DevAssert instead of goto/exit)

Create a new test scenario with USRP N310, 60 MHz bandwidth, 4 DL layers and
2 UL layers. Test 480 Mbps DL and 120 Mbps UL.

- simplify the code
- prevent to use "beta" tables from one decoder run to the next one (to see it
is the case, don't initialize beta, you will see it doesn't decode)
- decrease memory footprint of the decoder by x10 or more
- save about 15% of cpu in polartest unitary test tool, and more if we run in
realistic use case
- still this decoder performs much worse than the (very) slow OAI version by 3dB

telnetsrv uses the Intel/AMD-specific "cpuid" instruction, which is not
available on ARM machines. Remove the call.

The previous code was checking for the number of cores, which is
retained by a call to get_nprocs(). I did not find an equivalent for the
number of threads in C. In C++, there would be
https://en.cppreference.com/w/cpp/thread/thread/hardware_concurrency, in
case it's relevant for anybody.

Also, add it to the cross-compilation pipeline

use a better complex vector multiplication function